“There is no one way of doing things. There are only sound principles to adhere to. Understanding and applying these principles is the best place to begin.”




The key to maximum yield hydroponic gardening comes down to two key factors. These are environment and nutrition.

This means that an optimized nutritional regime along with optimized environmental factors such as light quality and intensity, air temperature, relative humidity, thermoperiod, root zone oxygen levels, CO2, water quality, pH, and EC need to be maintained at optimum levels in order to promote optimum growth – hence, yields.

As one US based nutritional chemist put it…



“Agree 100% – we have significant experience with other factors – light sources/exposure times, temperature, humidity, carbon dioxide, root oxygenation etc, and they are by far the most important factors – without their perfection nutrients beyond simple “Miracle Grow” are a waste of time.”

[End Quote]


There seems to be an obsession with focusing on the stimulants, additives, new and improved formulas, maximum yields through some new discovery, some new snake oil – some new claim! The only problem with this obsession is that we often overlook the simple things – the elements that nature provides. These are: oxygen, carbon dioxide, light, water, nutrition, temperature, and air humidity.

While these elements play a complex role in how they affect plants and what processes take place because of them, there are some very simple rules. Additives and snake oils will do absolutely nothing when one or more of these factors is significantly out of whack.  Get all of them right and you are 99.9% on the way to being a very successful indoor gardener.

Too often people ask me, “What product will give me a better yield?” I quiz them about ventilation, temperatures, nutrient, light, humidity etc. More often than not I get a vague stare…the sort of look that says – “All I wanted to know was which product will give me a better yield!”

Ideal conditions from start to finish. Optimum plant health from start to finish… That’s the secret to maximum yields. Light, water and air temperatures, nutrition, ventilation, carbon dioxide, oxygen, humidity levels, preventive practices that protect your plants from the onslaught of disease and pests – these are the things that enable the plants to perform at their best. Plant nutrition is only as good as the environment it is used in. That simple!!


Controlling Your Environment

As an indoor grower you are responsible for providing the wind, the light, the earth, and the seasons to your plants. This gives you an incredible amount of control over the very lifecycle of this living matter.

Ultimately, however, control is dependent on the knowledge that you possess, the approach that you take, and the equipment that you use for optimizing your grow room environment.

In many ways you are able to exert god-like influences over a small microenvironment. Such power enables you to produce results that nature (where lack of control can work against you) can never provide. Alternatively, undesirable practices can wreak havoc. Flood, famine, pestilence and plague are all too common in some grow rooms.

Experience in the hydroponics industry provides a broad insight into various growing philosophies. Some people approach indoor growing as a precise science while others approach it more pragmatically based on learnt experience (“I know what I know!”). Some people spare no expense while others sparingly shop for the cheapest equipment that they can find. Some indoor growers constantly reap excellent yields while others don’t do nearly as well.  Why?

If the indoor grower is capable of exerting god-like influence – how do some growers get it so right while others get it so wrong?

Consistency = Predictability

Control is the decisive factor in determining predictable yields. This is because control in the indoor grow room eliminates unknowns.

Fortunately, control is an easy matter.  Furthermore, you do not need to spend significant sums of money, nor be a rocket scientist to achieve desirable levels of environmental control in your grow room.


If I were to ask you what temperature is your nutrient kept at? What minimum and maximum temperatures do your plants receive in their daylight hours? What minimum/maximum temperature do your plants receive in their night time hours? What humidity levels exist in the grow room during night and day? And, what pH and EC (ppm) is the nutrient kept at? Would you be able to answer all of these questions without thinking too hard about them? Would you be able to answer them at all?

If I were to ask you what system checks you have in place to ensure continuity of favorable conditions, what would your answer be? Could you say things like a minimum/maximum thermostat/humidistat? Would you be able to tell me that you use a thermostat that controls when the exhaust fan switches on and off (based on temperature)? Or a second exhaust fan set on a timer so that it switches on during the plant’s night cycle and switches off during the plant’s day cycle? What about a thermometer that measures the water temperature? Or a water heater that keeps the water temperature at a constant favorable temperature?

What about other system checks such as preventive measures to avoid plant disease? What is your approach there? Do you have adequate airflow to minimise the chances of plant (airborne) fungi damaging your crop? Do you use friendly bacteria or sterilizing agents to prevent any water borne fungi (damping off fungi) attacking the plant’s root zone?

All of these things are of vital importance to ensure OPTIMUM CONTROL in your grow room environment!

When I pose these questions to indoor growers, their responses are generally vague at best. Typically, they will be able to tell me their grow room temperature – though not necessarily their maximum and minimum temperatures. Some of them will even know their water temperature. When quizzed further I may find out that their room temperature is monitored 5 foot away from the plants; they’ve got a thermometer stuck somewhere on a wall. I then suggest that they may like to monitor their temperature directly under the lights, and at plant height.

After all, the plants don’t care what the temperature is 5 foot away on the wall. The plants are directly under very hot, very intense lighting. The chances are it’s 5 – 8 degrees Celsius warmer under those lights than it is 5 foot away. If it’s 28 degrees Celsius (82. 4 ºF) on that wall (5 foot away), then it’s possibly 33 – 36 degrees Celsius (91.4- 96.8 ºF) under those lights. The difference being thrive or die. While genetics play a role in optimum temperatures it can be simply said that plants thrive at 24 – 28 degrees Celsius (75.2- 82. 4 ºF) – while the same plants will slow down growth and protect themselves at approximately 32 degrees Celsius (89.6 ºF). Long periods of excessive heat will eventually kill plants. Additionally, excessive heat reduces resin/essential oil production.

The thing is, when I ask these questions it is because someone needs assistance. Their leaves are yellowing, rusting, falling off. Or the roots of the plants are brown, tiny, rotting, and/or smell putrid. The plants don’t seem to be growing. Or the plants are simply dying. Hardly surprising! Being a god gives you the power of life and death!

Environmental factors need to be controlled. Water temperature, air temperature, air circulation and humidity are all vital elements where plant growth is concerned.

The Endless Perfect Summer

Too often I hear statements like, “I always get my best results between October and December.” Or “I always get the best results in summer because the plants know what season it is outside.” Or “ I always get my best results in winter.”

So what’s it to be? Winter or summer? Do the plants really know what season it is?

Well yes! If you tell them what season it is. You have the controls! You are god!

The only possible reason that the plants would know, for instance, that it was winter outside would be because you were bringing winter indoors through the use of too much exhaust.

The fact of the matter is, if you’re getting your best results within a set timeframe of the year, you ought to try analysing and mimicking those exact same conditions (in the grow room) all year round. Makes sense doesn’t it? Consistent results all year round. Consistency through environmental checks and controls! The endless, perfect summer.

Taking Control

The most functional grow rooms have a balance of smart technology combined with relative simplicity.

While the tech heads will get awesome results with their air-cooled light shades, their CO2 injection systems, and their automated pH and salts adjusters, it is not necessary to go to such extremes to refine your grow room environment.

While you may eventually build a room with every available device, it is not desirable for beginners to introduce this level of sophistication into their grow room environment. While learning, the KISS (Keep It Simple Stupid) principle is the safest practice. Should things not go quite to plan it is easier to analyse what is wrong when fewer more manual practices are involved in your growing practices. Automation and sophistication can sometimes create more problems than they’re worth. That is, simplicity = safety.

So what’s the basic gear that will enable you to control your environment?

Air Temp/Air Circulation

  • A thermostat (preferably one that registers temperature under the lights at plant height) that switches the exhaust fans on and off.
  • Adequately powerful exhaust fans to remove the hot air generated by HID lighting.
  • An inlet fan placed diagonally opposite the exhaust fan to ensure good spread of replacement air.
  • An oscillating fan which gently (I stress “gently”) pushes a breeze across the plants and moves hot air out from under lampshades.
  • In extremely hot climates, some form of air-cooling device may be necessary. For instance, if the ambient air temperature outside is 32 degrees Celsius (89.6 ºF) at night (you will probably be running your plant’s day cycle at night to help with temperatures) it is impossible to bring your room temperature down to the necessary 28 degrees Celsius (82.4 ºF) without some form of cooling.



  • A second exhaust fan (set on a timer) that runs during the plant’s night cycle. Plants transpire during sleep. This adds humidity to the environment. Plants also appreciate fresh air.


  • A quality pH meter. pH meters are scientific instruments. Treat them as such. They need to be regularly calibrated. The probe should be kept moist (preferably in pH meter soaking solution – tap water should also suffice). Treat them kindly.
  • (OR) A pH test kit.
  • pH Buffer solution to ensure that your pH meter is always calibrated. This will ensure accurate readings.
  • pH Up/Down.

EC/PPM/TDS (Food strength)

  • A quality salts meter.
  • EC standard (always ensure meters are correctly calibrated)


  • Regular replacement of lamps (at least once every 6- 8 months, but ideally after every two crop cycles) will ensure that your plants are receiving the optimum colour spectrum.
  • A good quality timer that runs the lights. An amazing amount of damage can be caused to the plants if the lights stay on for 24 hours for several days during the flowering cycle. Do not underestimate the value of spending decent money timing equipment. Most experienced growers know that cheap timers will eventually cost you more in the long run than initially purchasing quality timing gear.



  • Good air circulation and reasonable humidity levels are the best way to avoid fungal disease in the leaf material.
  • Use a silica (Si) product during grow and bloom. Silica increases resistance to pests, fungi and disease. Additionally, silica is shown to benefit resin production and yields. (more information on silica can be found here...)
  • A preventive spray with an anti-fungicide from time to time is a good practice to get into.
  • Waterborne fungal diseases (pythium etc) should be prevented with either sterilization or the introduction of friendly bacteria into your nutrient system.



  • Close monitoring for pests is the best way to prevent crop damage. While you can’t necessarily keep pests out of your grow room you can keep your plants safe from any potential damage. Shake the plants occasionally to see if any flying pests (white fly, scarid fly etc) are present. Look under leaves for tell tale signs of pests such as spider mites (tiny black dots on under leaves).
  • Many different sprays and predators are available on the market to eliminate or control pest numbers.  Keep them handy.
  • Use a silica (Si) product during grow and bloom. Silica increases resistance to pests. (More information on silica can be found here…)

What this all comes down to is that, across the board, successful indoor growers who consistently get big yields are willing to spend time in their grow rooms, invest in the right equipment, and spend the necessary dollars on quality equipment and products. Furthermore, they remain open minded about new and improved methods of cultivating plants. They do not get stuck in their ways, but carefully embrace new technology and information. Quite simply, they approach indoor growing like professionals.

On the other hand unsuccessful growers tend to think that they can get away with saving money by not using preventives, not buying equipment that can refine their grow room environment and by saving $10.00 on that cheaper meter etc. The only problem is that they are prepared to take a chance (even if they don’t know it) at the risk of compromising their plants.  Often the unsuccessful grower is dogmatic about ways of doing things, thinks everyone who is trying to explain why a product should be used is scamming him/her, and generally exercises sloppy practices in their grow rooms.

As a beginner, it is reasonable to expect that you may have some failures. This is not necessarily through any philosophical fault of your own. You are learning, and part of learning is making mistakes. However, if you continue to make mistakes you might want to question your approach and/or philosophy to indoor growing.

Grow Room Optimums (air temp, humidity, water/media temps, CO2, pH, EC etc)

Air Temperature


In nature temperatures can be very inconsistent. When the ambient air temperature is too high or too low a plant will reduce the chemical processes that take place in order for it to grow. In short, if the ambient air temperature is too high or too low a plant will not achieve optimum levels of growth.

Genetics will influence ideal day temperature ranges and some experimentation is advised (know your genetics). However, as a safe generalization, all genetic varieties thrive between 25- 31 ºC (77 – 87.8 ºF) – a standard (safe) recommended temperature range being between 26 – 29 ºC (78.8- 84.2 ºF).

It is important to note that plants will stop growing or significantly reduce growth rates to protect themselves against excessive heat. In addition, studies show that essential oil/resin production goes down as the temperature goes up, so it is important to ensure that optimum air temperatures are maintained throughout the grow and bloom cycles.

Overly cool growing environments will result in the slowing of the metabolic processes of a plant and, as a result, growth rates (photosynthesis) will be reduced. Daytime temperatures should never be allowed to fall below 23 ºC (73.4 ºF).

THERMOPERIOD (Night vs. Day Temps)

Thermoperiod refers to daily temperature change. Plants produce maximum growth when exposed to a day temperature that is about 10 to 15°F higher than the night temperature. This allows the plant to photosynthesize (build up) and respire (break down) during an optimum daytime temperature, and to curtail the rate of respiration during a cooler night. High temperatures cause increased respiration, sometimes above the rate of photosynthesis. This means that the products of photosynthesis are being used more rapidly than they are being produced. For growth to occur, photosynthesis must be greater than respiration.

However, not all plants grow best under the same range between nighttime and daytime temperatures. For example, snapdragons grow best at nighttime temperatures of 55°F (12.77°C); poinsettias, at 62°F (16.66°C).

Other than this, genetics (different genetics of the same species) have been shown to play a role in thermoperiod optimums. For instance, a strain from Afghanistan (warm days and cold nights) will respond more positively to cooler nighttime temperatures than strains that originate from tropical climates such as Malawi or Thailand (warm days and nights).

What this means is that some experimentation is advised; however, in all instances night temps need to be lower than day temps in order to achieve optimum yields.

As a rule of thumb day temperatures should be approximately 5 – 8°C higher than night temps.

The gap between night and day temperature should never exceed 10°C.



Light plays a very important and complex role in photosynthesis. Light is the energy of photosynthesis; it powers all aspects of plant growth. Without light there would be no green plant life on earth.


Energy = Energy


Photosynthetic levels determine growth rates and light is the energy of photosynthesis.


Light is primarily responsible for creating chemical energy (in the form of glucose) in plants. Glucose then becomes the fuel for other agents of plant growth.


This process is called photosynthesis. Photosynthesis is the fundamental food making process in all green plants. Light is the energy source for the complex chemistry of photosynthesis.


In a nutshell: The plant takes in water from the growing media and carbon dioxide (gas) from the air, and in the presence of chlorophyll it makes the simple sugar glucose, which is now the store for light energy. In this process oxygen is separated from the water and passes out into the air.


Glucose is the building block for several other sugars and complex carbohydrates that the plant makes (eg. fructose, sucrose, starch etc).  The glucose is stored in the leaf tissue. In addition to this, it is the leaves that catch and trap the light energy. Therefore, leaves receive light and store it as chemical energy.


While photosynthesis is very complex we can summarize it as:


Water + Carbon dioxide + light energy in the presence of chlorophyll = Sugar + Oxygen + Water


Photosynthesis consists of two separate cycles; one of which occurs in the presence of light (light hours), the other in the absence of light (dark hours).


To understand these two processes consider that the plant, in the first phase of the cycle (the light cycle), traps light and stores it as a simple form of chemical energy (glucose).


The night cycle, on the other hand, can be described as the conversion of this simple chemical energy into a more sophisticated form of chemical energy (sugars and complex carbohydrates). The plant uses this chemical energy for growth.


The light energy required by plants is confined mostly within the visible spectrum of light (400nm – 700nm). This said, while there are two key points within this spectrum (435nm and 675nm), growth is optimized under the entire range of the spectrum, including non-visible UV-b radiation and UV- a radiation (280- 315nm).


This is because different colour wavelengths stimulate different biochemical reactions within the plant. As a result of this, different physiological functions are activated and energized, which – in turn – determine plant growth rates, formation characteristics, and resin/essential oil production (quality). For instance non-visible UV-b radiation and UV- a radiation, while not being visible in the spectrum, are shown to increase quality (eg. UV-b is shown to be a specific regulator of gene expression and metabolite profiles).


Photosynthesis depends on the energy created by a combination of both light intensity and colour.


Growers who have experimented with different lighting combinations can/will tell you that different lighting configurations can produce very different results. For instance, plants that are flowered under a combination of red spectrum (HPS) and blue spectrum (MH) lighting form very differently than plants that are flowered under red spectrum light alone.


For example, a plant that is flowered under HPS light alone typically ‘stretches’ (becomes unnaturally elongated). This is because, while HPS provides large amounts of yellow and red light it tends to be lacking in other key areas of the visible colour spectrum. This means that the required stimulus for the various biochemical responses is not adequate.


By introducing blue spectrum light into the red spectrum we are able to cater more adequately for these biochemical responses. In short, blue spectrum light promotes a better plant structure (shorter/stockier plant, smaller gaps between nodes) while the red/yellow spectrum light provides stimulus for flower growth.




One of the most common mistakes made by indoor gardeners is that they fail to appreciate that fewer plants can mean more yield. Too many plants crowded into a small space will compete for available light and as a result stretch as they compete. Other than this, plant crowding will result in all of the plants shading the bulk of one another out, which in turn will result in each and every plant performing well below optimum photosynthetic potential/levels.

CO2 and Ventilation


Plants use Carbon Dioxide (CO2) in photosynthesis. Without CO2 photosynthesis, effectively, ceases. Carbon Dioxide is absorbed through the stomata of the plant and is essential for healthy growth. In any enclosed growing environment the air needs to be constantly exchanged to make sure adequate CO2 is available, as it is very quickly used up by rapidly growing plants. Air movement (ventilation and circulation) is therefore critical to ensure adequate levels of CO2 are available in the grow room atmosphere.

As of November 2011, carbon dioxide in the Earth’s atmosphere is at a concentration of 390ppm by volume.

However, plants benefit from much higher levels of CO2 than is naturally present in the atmosphere. Research has shown that C3 plants have a CO2 saturation point of between 1000- 1500ppm, with 1200- 1250ppm likely being the most suitable range for indoor crops.


Light and CO2 Relationship (In Brief)


There is a symbiotic relationship between light levels, light color spectrum and CO2.


Several things will determine the benefits of additional CO2.


Light Levels (lumen): Plants require a given amount of light lumen in order to utilize extra CO2. There would be very little point in providing additional CO2 to a plant under extremely low light levels. Under HID lighting situations extra CO2 can be very beneficial to growth due to the high lumen output of most HID lamps. Increasing CO2 levels means the plant is able to absorb and utilize more light.  This increases growth rates.


Light Color: Strong blue and red photons are required for maximum uptake/use of CO2.


Critical Mass: Think of the plant as a growth factory. The factory can only operate so efficiently. The machinery of photosynthesis (the chloroplast*) has its limits. There comes a point where more CO2 and more light simply go to waste.


*Chloroplast Definition: A ‘plastid’ (any of several pigmented cytoplasmic organelles found in plant cells and other organisms, having various physiological functions, such as the synthesis and storage of food) that contains chlorophyll and is the site of photosynthesis.

Relative Humidity, Temps, Photosynthesis, and CO2


Relative humidity (RH) is a term used to describe the amount of water vapor in a mixture of air and water vapor.

High relative humidity can promote the incidence of fungal disease and reduce the plant’s ability to metabolise. 40 – 60% RH is the optimum range to promote healthy growth.

In addition, in order to have carbon dioxide available to the stomata reasonable air temperatures and humidity levels are required.

Excessive temperatures reduce chemical/photosynthetic activity within the plant.

Similarly, excessive humidity will reduce the plant’s capabilities to process CO2. This is because moist air suffocates the stomata, reducing its ability to collect the necessary amounts of carbon dioxide needed for optimum growth. In addition, moist air reduces the plant’s ability to transpire. Transpiration is the movement of water from the roots to leaf surface – driven by evaporation. At high humidity, evaporation is low so transpiration slows down. As a result of this, growth is adversely affected.

ROOT ZONE HEALTH – Nutrient and Media Temperature


Healthy Roots equate to healthy plants and growth rates.

Temperature affects the root system differently from the stem, leaf and flower structures. Excessive water temperatures will reduce available oxygen to the root zone. The root system can become damaged as a result, which in turn affects the plant’s ability to uptake nutrition. Oxygen starvation as a result of excessively warm water is the key reason for root rot in hydroponic systems.

Nutrient salts don’t leak into the roots of the plant. Nutrient uptake is an active process that relies on several factors, one of which is that satisfactory levels of oxygen are available to the roots of the plant.

Roots “pump” nutrients from the outside of the root to the inside where they are transported to the leaves. This pumping process requires energy. The roots get their energy from respiration. In turn, respiration requires energy, which is achieved by burning sugar. Part of the sugar made in leaves by photosynthesis is transported to the roots to power the nutrient pumps.

Photosynthesis converts sugar and oxygen from carbon dioxide, nutrition and water using the energy from light.

Respiration is the opposite. Respiration makes energy by burning sugar (supplied by the leaves of the plant) and oxygen to make carbon dioxide. It is this energy that powers (among other things) the root nutrient pumps. In turn these pumps deliver the nutrition that is critical to sugar production within the plant.

Unlike sugar, oxygen is not transported from the leaves to the roots. This means that the roots must get their own oxygen.

If the roots can’t get sufficient amounts of oxygen (because of excessively warm water/nutrient or because there isn’t enough air space in the growing medium) their pumping capacity is significantly reduced. The result of this is that the plant becomes starved of critical nutrition.

Roots are just like people. If they can’t get oxygen they suffocate.

Optimum Water/Nutrient Temperatures


While there is a complex relationship between air pressure, water salinity (ie. fresh/pure water can hold more oxygen than saline water), temperature and oxygen it can be simply stated that fresh water (non saline) can hold approximately 8.26 parts per million of oxygen at 25OC (77 OF), while at 20O C (68 OF) water can hold as much as 9 parts per million of oxygen. This said, given hydroponic nutrients contain salts (are saline), in the form of nutrient salts, a working solution at 25OC (77 OF) holds approximately 5ppm of oxygen, while at 20O C (68 OF) approximately 8ppm of oxygen will be present.

Put simply, the colder water gets the more oxygen it can retain. The warmer water gets the less oxygen it can retain. However, if water is too cold the plant will stop taking up food. Therefore, a balance needs to be achieved between ideal temperatures for nutrient uptake and ideal temperatures to ensure adequate oxygen is available to the roots of the plant.

The ideal water/nutrient temperature for oxygen availability and nutrient uptake is between 20-22 0C (68- 71.6 0F).


The graph below illustrates the relationship between temperature and oxygen in water.

Root Zone Health Through Pathogen Preventatives


When science first conceived of hydroponics it was believed that the new artificial growing method would exclude soil borne pathogens. This was quickly disproven and it was soon discovered that a microflora, similar to that found in soils, rapidly established itself in hydroponic systems. Among the microflora were the plant pathogens Pythium, Phytophera and Fusarium.


Phytophthora (pronounced Fy-tof-thora – meaning plant destroyer) is a water mould, also known as an oomycete.

Phytophthora is an aggressive plant pathogen. When a plant is infected, it is unable to absorb nutrients.

Fusarium oxysporum

Fusarium oxysporum is a common soil fungus, and can become a pathogen causing a wide variety of wilt diseases in plants (usually called Fusarium wilts). Fusarium wilt can be identified with symptoms such as wilting, chlorosis, necrosis, premature leaf drop, browning of the vascular system, stunting, and damping-off.


The most common root disease found in hydroponics is caused by Pythium. Pythium attacks the root system and severely limits the plant’s capacity to uptake food. What this ultimately means is an unhealthy crop and a low yield. In severe cases it can lead to crop death.

Pythium can take hold of a weak, stressed crop far more easily than it can a healthy crop. Making sure that your plants remain healthy through the correct nutrition (particularly during heavy fruiting) and optimum conditions (air temp, water/nutrient temp, RH etc) will give your plants increased resistance against Pythium. I.e. plants grown in optimal conditions (i.e. optimal air temperature, optimal water/nutrient/media temperature, optimal nutrition, optimal RH) will be more resistant to root disease than plants that are subjected to stress as a result of less than optimal growing conditions.

This said…the prevention of pathogens is an easy matter.

There are two basic types of prevention.

A)  Sterilisation.

Products such as hydrogen peroxide, monochloramine, or chlorine are useful sterilising agents. Because water borne pathogens are living organisms, sterilisation will kill the spores before they have a chance to enter the plant’s root zone.

B)  Friendly Bacteria and fungi.

In nature, non-harmful, beneficial bacteria and fungi naturally combat waterborne pathogens. Generally speaking beneficial bacteria and fungi numbers grow at a faster rate than harmful organisms such as Pythium. As the non-harmful bacteria numbers explode they form biomass around the rhizosphere (root system) of the plant. This biomass prevents harmful organisms entering the rhizosphere of the plant.

More on this subject can be found here….



pH refers to the acidity or alkalinity levels of the nutrient and media. Having the correct pH will ensure that all the elements of the nutrient are available to the plant. The recommended range in hydroponics is between pH 5.5 – 6.1. A midway point is advisable. pH 5.8 being about optimum.


Soil pH


Soils optimum pH range differs to that of hydroponics. The ideal pH range in soil is typically stated as between pH 6.5 – 7.0. pH 6.7 – 6.8 is optimum.


EC (Electric Conductivity) and Nutrient Salts


Nutrient Salts refer to the levels of food available to the plant. In very simple terms, the larger a plant, the more food it needs.

It is important to note that all ppm meters first measure in EC (electric conductivity) and then run a conversion program to display the reading in ppm. There are three different standards used for EC to ppm conversions. These can be simply stated as:

USA 1 ms/cm (EC 1.0 or CF 10) = 500 ppm
European 1 ms/cm (EC 1.0 or CF 10) = 640 ppm
Australian 1 ms/cm (EC 1.0 or CF 10) = 700 ppm

For example,

Hanna, Milwaukee 1 ms/cm (EC 1.0 or CF 10) = 500 ppm

Eutech 1 ms/cm (EC 1.0 or CF 10) = 640 ppm
Truncheon 1 ms/cm (EC 1.0 or CF 10) = 700 ppm

For this reason, it is best to discuss nutrient salts in terms of EC (an international standard) and allow you to convert EC to ppm based on the standard that your ppm meter uses for conversion.

Below are some recommended EC values for the varying stages of growth and bloom.

It is important to note that these are approximate (near ideal) values only. The genetics of the plant, the size of the plant and the type of growing media/system in use will play a part in determining optimum nutrient EC. Some experimentation is advised to establish optimum EC for your particular genetics and growing methodology.



When you really think about it, once you have created the right environment, provided the right nutrition, and optimized everything in the grow room the rest comes down to water. Plain old water! Hydroponics at this point becomes 99% H20. So, let’s have a look at water.

It’s important to note that nitrate, ammonium, potassium, calcium, magnesium sulfate, and iron are all elements that are found in hydroponic formulations and depending on their levels in the feed water supply this will dictate how an optimized nutrient program is formulated.

Firstly, there is 0.78 EC (ms cm -1) of salts in this water supply and other supplies can/will contain even more elemental salts.

What this means is that the mains water in use in the hydroponic system begins with a relatively high degree (EC/ppm) of salts. For instance, if you were to begin with a tap water supply that contained 1 EC (500ppm) of salts and you were to grow with a total EC of 1.8 (nutrient in water) there would be minimal levels of balanced food salts available to the plants.

The only way to give the plants more balanced food is:

1) Up the EC to 2.0 – 2.2 (not a good option)

2) Reduce the existing salt levels in the water supply through using demineralised (RO) water

3) Formulate the nutritional regime with the water in mind and factor in the existing elements that are present in the water supply

Sodium (Na) and chloride (Cl) at bottom of water analysis table are the constituents of common salt. These normally occur together (i.e. sodium chloride = NaCl) and are not taken up to any degree by most plants, especially sodium. Therefore, they tend to accumulate if present in high amounts.

You will note that we have 161ppm of sodium and 202ppm of chloride in our water analysis. Sodium chloride (NaCl) can be toxic at even 50ppm to some plants (e.g. lettuce) while tomato plants can tolerate approximately (or over) 200ppm of NaCl.

Note: In some plants, levels of Na will partially substitute for K, thereby potentially enhancing fruitset.  It has been suggested that adding Na to a hydroponic nutrient solution at 30 to 50 ppm during mid to late flower, will enhance fruitset. Several bloom products we have tested contain levels of sodium. Either way, 161 ppm of sodium in the water supply is through the roof and if you were to factor in more sodium, via an additive, things may go pear shaped very quickly. I.e. Excess levels of sodium can lead to dehydration, reduced turgor, and cell death. Cell membrane integrity can be reduced as sodium displaces calcium, and water and nutrient uptake can subsequently be negatively impacted. Sodium can reduce protein synthesis and alter hormonal activity.

Other elements that can cause problems are:

Iron (Fe): Although iron is a micronutrient, in this form (in non chelated form) it can rapidly oxidise and precipitate as rust, which makes it unavailable as a nutrient.

Calcium (Ca) and Magnesium (Mg): These are constituents in hard water. As major nutrients they are useable in the nutrient solution. Their presence (if choosing to use mains water) should be allowed for in calculating precise nutrient formulations.

Bicarbonate ( HCO3 ): is also a constituent in hard water. It is alkaline and will raise the pH. It will need to be neutralised by acid, typically phosphoric or nitric. The amount of equivalent phosphorus or nitrogen added should be allowed for in calculating precise formulations.

Boron (B): Boron is the micronutrient with the narrowest range. If present in the water it can be omitted from your formulation. It can become a problem if its concentration is over 1ppm, or lower for sensitive crops. Boron only occurs in a few water supplies.

Mains Water Analysis on North American and Australian Water Supplies


Tests carried out in the US and Canada in 2006 on water hardness (calcium concentrations) demonstrated that water in Vancouver (by average) contained 1.4mg/L of calcium while water in Phoenix (by average) contained 82-180mg/L of calcium.

The Canadian tests found that Toronto had 34mg/L, Kitchener had 135.5mg/L, Waterloo 125.9mg/L, Vancouver 1.4mg/L, Montreal 32mg/L, and Halifax 6.8mg/L of calcium present in their water supplies.

US tests in 33 regions/cities demonstrated that US drinking water supplies ranged from 8.2mg/L to 82-180mg/L of calcium. By the way, many of these tests needed to be averaged due to multiple water supplies in any one city or region.

Tests carried out in Sydney, Australia, on nine separate water supplies demonstrated total water hardness (magnesium and calcium as mg CaCO3) variants of between 6-36mg/L in Illawarra to 52 – 62mg/L of mgCaCO3 in the Cascade’s supply.

Breaking this down even further and looking at best to worst case scenarios, sulfate levels in the 9 water supplies ranged from 1 – 3mg/L to 38.9 – 65.3 mg/L; sodium levels from 4.1 – 14.8mg/L to 38.9 – 65.3mg/L; chloride levels from 15.0 – 26.5mg/L to 55.5 – 74.0mg/L and potassium levels between 0.78 – 2.02 to 2.81 – 6.62mg/L.

You will no doubt note the differences between water supplies in a single city. This situation isn’t uncommon and if we were to go on a state-to-state basis we would find even greater disparities.

Additionally,  if you were  to test the same mains water supply several times over the course of a year the water supply would probably change (in some cases significantly) on a test-by-test basis. That is, the same water supply’s macro and microelements would differ on each test. This means that to ensure optimum crop specific nutrition you would either need to continually lab test your mains water and formulate accordingly or work with a more consistent water supply.

The bottom line…..

Technically speaking (from an agricultural science perspective) an optimized nutritional regime is formulated through establishing and meeting set (ideal) nutritional targets (ppm on delivery) of each element that the plant requires for the various stages of growth. This is something that “hydro” manufacturers typically forget to mention with some going so far as to state that their products are formulated for e.g. Australian water supplies. We’ve just looked at 9 water supplies in a single city, so the claim that a single formula can be made for vastly differing water supplies is largely misleading.  I.e. Formulas for hard water – how hard is the water etc?

So how to get decent water?

Reverse Osmosis Water Science for Hydroponics  


By treating mains/tap water via RO filtration mineral salts are removed leaving you with pure, salt free water. The use of RO water is advisable for achieving consistently optimum yields in hydroponic settings.

The major advantage of removing the existing salts from your hydroponics water supply is that it ensures your plants are getting only the best salts. That is, salts that are blended for the purpose of plant growth (in the form of nutrient).

Tap water is that the salts are very random and (mostly) not suitable for plant growth. When you mix nutrient with tap water the balance can be a bit out of whack due to the combination of tap water salts with nutrient salts. Then as your plants uptake water and nutrients, the salts change further.

If you top up your tank with tap water (a combination of salts and H2O) and then add more nutrient to bring the salts back to desirable (EC) levels this further throws the blend of salts out of balance.

Eventually you will end up giving your plants completely imbalanced nutrition. This can result in your plants burning due to the imbalanced food that they are receiving. At best their vigor will be affected by various deficiencies and extremes. This is why – if you are using tap water – you should only top up your nutrient tank (in a recycling system) with water and not add further nutrient salts.

By using de-mineralised  (salt free) water you are able to ensure that your plants are receiving the correct balance of salts/food between tank changes. Furthermore, because there are no mineral salts in the water, you are able to add water (top up the nutrient tank with water) and nutrient (then add nutrient to the desired salts (EC) level) with every top up of the nutrient tank. Because of this the plants are constantly receiving optimum nutrition. In addition to this, the necessity for nutrient dumps (complete water and nutrient changes) is greatly reduced.

To understand Reverse Osmosis (RO), it is necessary to understand the process of osmosis. In living things, osmosis is frequently seen. The component parts include a pure or relatively pure water solution and a saline or contaminated water solution, separated by a semi-permeable membrane.

The semi-permeable membrane is so designated because it permits certain elements to pass through it while blocking other elements. The elements that pass through the membrane include water, usually smaller molecules of dissolved solids, and most gases.

A fundamental scientific principle now comes into play. That is, dissimilar liquid systems will try to reach the same concentration of materials on both sides of the membrane. The only way for this to occur is for the pure water to pass through the membrane to the saline side of the membrane.  This attempt to reach equilibrium is called osmosis.

In the early 1950’s an Indian scientist (Sourirajan) working at the University of California discovered that by reversing osmosis saline water could be purified. This was achieved by reversing the natural osmotic flow and forcing salt water, under pressure, through a permeable membrane. Through this process tiny water molecules were able to penetrate the membrane while larger salt molecules remained outside the membrane.

By collecting only the water that had penetrated the membrane an almost pure H20 product could be obtained.

The EPA recommends reverse osmosis as the most satisfactory technology for removing dissolved impurities from water. With the exception of distillation, reverse osmosis is the only known process that will effectively remove turbidity, sediment, colloidal matter, total dissolved solids, toxic metals, radioactive elements, pesticides and herbicides.

The energy (to output ratio) used for reverse osmosis is far superior to that of distillation. The only energy required is mains pressure which forces the pure water through the permeable membrane. Distillation, on the other hand requires high energy usage to water output as it is necessary to boil water through the use of electricity or some other form of energy such as gas.

Rainwater, while not requiring energy to output, still contains some degree of sediment and impurities. Another obvious disadvantage of using rainwater is the need for a large water tank.


Lab Analysis of RO Water

You will note in the lab test of Reverse Osmosis water that a total EC of 0.02 is present. There is 1ppm of calcium, <1ppm of magnesium, 10.96ppm of bicarbonate, 2.07ppm of sodium and 2.13ppm of chloride. In very simple terms this is a vast improvement over our earlier mains water lab analysis example where there was 41.9 ppm of calcium, 14.4ppm of magnesium, 161ppm of sodium and 202ppm of chloride (extreme levels of sodium chloride)


Additionally, if I were to test any mains water treated with Reverse Osmosis, no matter what elements were present in the mains supply, at what levels, the RO treated water would remain consistent due to removing these elements during filtration.  What this means is consistently pure water every time.

However, there are a couple of things that you need to be aware of in order to get the best results with RO water.

RO Water and pH Stability


RO filtering of mains water not only removes undesirable compounds but can also remove desirable compounds in the form of bicarbonates (HC03) and carbonates (CO32-) which create a natural pH buffering system via adding alkalinity to water.  Ideally it is best to correct this after RO filtration using sodium bicarbonate (baking soda) or another carbonate or bicarbonate product (e.g. potassium bicarbonate, calcium carbonate etc). We’ll talk more about this in a second.

What is Alkalinity?


Alkalinity is the buffering capacity of a water type. It measures the ability of water to neutralize acids and bases thereby maintaining a fairly stable pH. Water that is a good buffer contains compounds, such as bicarbonates, carbonates, and hydroxides, which combine with H+ ions from the water thereby raising the pH (more basic) of the water. Without this buffering capacity, pH can become unstable.


Correcting/Creating Alkalinity in RO Water With Carbonates 



This one only applies to those of you who are using RO water and relates to water alkalinity and its ability to buffer pH. For those of you who are using mains water this material doesn’t apply due to mains water often possessing high alkalinity (often far too high) values. Alkalinity is best expressed in this case (so as not to confuse things) as the buffering capacity of water. That is, the alkalinity of water is related to the pH, but it is actually a different parameter. It is a measure of the capacity of the water to resist changes in pH. Don’t confuse “Alkalinity” with “Alkaline” (which relates to an alkaline pH of above 7.0). The higher the alkalinity, the more acid can be added without considerably changing the pH. This is because the bicarbonates (HCO3) and carbonates (CO3-2) react with the hydrogen ions (H+) contributed by the acid, preventing them from dropping the pH. Alkalinity is typically expressed as the equivalent concentration of calcium carbonate (CaCO3). The ideal range for alkalinity as ppm CaCO3 is expressed as 40-60 ppm, with 20-80 ppm being the outside range. Calcium carbonate is 60% carbonate and 40% calcium at 100% purity. Thus to equate 60 ppm CaCO3 into how much carbonate this represents 60 (ppm) – 40% (calcium) equals 60% Carbonate, so 60% of 60ppm = 36ppm carbonate. This would equate to 1 gram per 10L of water using calcium carbonate or when using potassium carbonate (K2CO3 is 43.4% carbonate @ 100% purity) 0.83 grams per 10L or when using baking soda (sodium bicarbonate or NaHCO3 which is 76.24% bicarbonate) would equate to 0.762 g/10L.  As a recommendation, I tend to suggest that baking soda is ideal for increasing alkalinity in hydroponic systems where RO water is used. Firstly it is easy to access at high chemical purity through supermarkets. Secondly, when used at the suggested rate of 0.47grams per 10 litres it contributes approximately 13.5ppm of sodium (Na) to the nutrient solution which is well within tolerance range for plants being grown in hydroponic systems (and less Na than is typically found in mains water supplies). On the other hand, while some have recommended the use of potassium carbonate and calcium carbonate for pH buffering water, both of these components will add calcium or potassium to the working solution at ppm which may contribute to nutrient imbalances.


It is important to note that in equating the grams per 10L required for buffering I established these values though using calcium carbonate, potassium carbonate and sodium bicarbonate at 100% chemical purity. Typically, however, chemical purity will be somewhere between 97-99.5% purity. For example, baking soda (food grade) is typically about 99% purity. However, the fractional differences in purity (i.e. 100% to 99%) will equate to a minute drop in ppm values which will have no influence whatsoever. Other then this, for the chemistry purist, I haven’t equated moisture content (MC – an unknown quantity given the various chemicals and sources/supplies) which is why I worked at the higher range of the alkalinity requirement for hydroponic system water to compensate for MC.


When you purchase any of the aforementioned chemicals, 1) always attempt to find out the purity of any carbonate product you are using for pH buffering and; 2) if the chemical purity is at anywhere between 97-99% use the grams per 10L I have recommended.

By the way, when using a carbonate product to buffer RO water the pH will rise and this will need to be corrected to bring pH into line with optimum (i.e. pH 5.8-6.0). To do this I highly recommend that citric acid is used as a pH down because this will add further buffering capacity to the solution and provide carbohydrates (which aids the krebs cycle) for the beneficial bacteria and fungi in your system.

Cal Mag Product Use in RO Water


RO filtration removes calcium and magnesium from the water supply. For this reason you may find that this needs to be compensated for through the use of a cal mag product (e.g. Manic Botanix RO Perfect which also handles the buffering/alkalinity correction for you – hence no need for sodium bicarbonate).

For instance, Canna Coco Nutrient is formulated for hard water supplies (water supplies that contain high degrees of calcium and magnesium) so when using Canna Coco nutrients with RO water, for optimum growth, the addition of cal mag is required.  You may wish to seek further information from your hydroponic supplier or nutrient manufacturer regarding whether they advise the use of ‘Cal Mag’ when using their products with RO water.



Optimum yields rely on optimum plant health throughout the entire lifecycle. Plants that have been stressed at any point of their lifecycle rarely achieve genetic potential.

Use additives to prevent root disease and oxygenate the water/nutrient to prevent oxygen starvation (hence root disease).  Avoid fungal disease through adequate airflow, the use of silica, and, if need be, other preventative measures. Prevent problems through ensuring that environmental parameters are running at optimum (I.e. temp, RH, pH, EC etc are maintained at optimum levels).



Pests in the grow room can cause serious damage to your plants.

It is important that pests be spotted early to minimise potential damage. This is critical because, in the case of most insect varieties, numbers can explode very quickly.

When dealing with pests it comes down to proactive growing practices. That is, tackling a problem before it becomes a problem. For instance, there is very little point noticing the presence of Spider Mite at the point that their webs are covering your crop. If this were the case your plants would already be severely damaged.

Simple early warning systems such as placing yellow sticky traps in your room (particularly near entry points… eg. air inlets) will help you pick up the presence of unwanted bugs before things get out of hand.

Similarly, checking your plants for insects should be a weekly ritual. Examine the tops and undersides of leaves as an early means of detection. Look for signs of leaf damage (rust like spots, silver residue on leaves and deformities etc) and for the insects themselves.

Prevention is always better than cure. Spray your room for pests before every new crop cycle. Bug Bombs are handy for this. Simply let a couple of bug bombs go while there are no plants in the area.

In addition to this, treat any cuttings before they go into the growing environment. One of the most common ways of getting pests is that they come in on cuttings that other people have provided.

(More on growroom pests can be found here) 



Plant Genetics play, by far, the most important role in the final quality and quantity of the produce (once the essential elements are refined).

If you begin with mediocrity you will finish with mediocrity. That simple!!

Finding the right genetics and ensuring continuity of these genetics in future crops will ensure (along with environmental factors) fruitful and bountiful results.

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