Si and Value for Your Money


The point of purchasing a silica additive is to provide silica to your plants.


Thus, the quality of a silica product for use in hydroponics comes down to the amount (%) of plant available silica (PAS) that any given product provides. This can be accurately measured using the 5-day method for determining the soluble Si concentration.


Currently, the Californian Department of Agriculture is working towards standardizing this test for listing Si percentages on silica product labels. This is being done so that consumers are able to evaluate just what they are getting for their money with regards to plant available silica in any given silica additive.


Below is a table showing the plant available Si percentages in various silica products that are available through hydroponic stores and/or agricultural suppliers. All tests conducted using the 5-day method for determining the soluble Si concentration.


Manufacturer Fertilizer Name Total Si % Plant Available Si% (Soluble Si)
Med-Tek Super Silica 30% 14.1%
PQ Corp Agsil 16H (K Sil Powder) 24.6% 8.54%
PQ Corp Agsil 25 (K Sil Liquid) 9.7% 7.6%
Plant Science Concepts OSA 28 (PEG 400 Stabilized Silicic Acid) 2.09% 1.06%
Mills Vitalize 0 – 3 – 1 0.94%
Fertimaster Power Si (PEG 400 Stabilized Silicic Acid) 1.71% 0.88%
Aptus Fasilitor (PEG 400 Stabilized Silicic Acid) 1.61% 0.85%
Loveland Products SST 28% (Stabilized Silica Technology) 0.44%



You’ll note on top of the list is our product, Med-Tek Super Silica. You’ll also note that this product tested at by far the highest percentage of ‘plant available Si’ at 14.1%. The next highest testing product being Agsil 16H ‘K Sil’ (potassium silicate) powder which tested at 8.54%, or 5.56% less PAS than Med-Tek Super Silica.


What this means is that value for money wise, where looking to supply plant available Si to solution, Med-Tek Super Silica is by far the best brand/product option given purchase price and PAS percentage.


Recommended dilution rate is 3ml per 10 litres of nutrient solution (60 ml per 200 litres). This provides 42.3 ppm of plant available Si to the hydroponic solution. 1 litre of Med-Tek Super Silica treats 3,333 litres.


Claimed to be Stabilized Silica Products


We hate seeing growers being scammed out of their hard earned cash so there’s something that needs to be said regarding just a few silica additives that are being peddled through some hydroponic stores.


There’s recently been a big push, with bells and whistles marketing, by a couple of commercial interests to flog high priced, claimed to be stabilized silica products. These products are sold to consumers with what can only be described as dubious marketing. Take for example Super Si (available in Australia through Stealth Gardens) and Power Si (available in Australia through Power Si) which are being pushed hard to Australian growers through glossy advertising, replete with wondrous claims.  For example, the marketing jargon for Power Si on the supplier’s website states:




“Power Si is the original patented form of stabilized, bioavalible silicic acid for crops. Unlike other silica products, we work with the best possible silicic acid matrix (patented!) to ensure superior absorption. Power Si is a proprietary organic biomix containing highly bioavaliable micro and macro nutrients. It is a pure, highly concentrated formula with fast visible effects.


[End Quote]


Note, “Power Si is a proprietary organic biomix containing highly bioavaliable micro and macro nutrients. It is a pure, highly concentrated formula.”


Firstly, using the word “organic” is at best highly questionable, at worst, scurrilous. Power Si contains PEG 400, potassium sulphate, boric acid, phosphoric acid, sodium molybdate and monosilicic acid (presumably derived from potassium silicate), all of which are inorganic chemicals and most of which cannot be used as organic inputs in agriculture (although a couple of them might pass as organic inputs under certain strict conditions with some organic registration bodies). However, for example, PEG 400 is an artificial, fully synthetic petrochemical which is only biodegradable under certain conditions (e.g. water treatment plants, industrial compost) and is readily assimilated by plants and ends up unaltered in the final, harvested product. Bottom line….. Power Si is not organic in any way, shape or form unless. of course, you consider petrochemicals organic.


Then there is “It is a …. highly concentrated formula.” Nope! No it isn’t! We’ll demonstrate why this product is anything but concentrated in a moment.  For now….


Super Si is being flogged at between $60.00 for 100 ml to $400.00 for 1 litre while Power Si is being peddled for approximately $80.00 for 250ml or about $260.00 for 1L in Australia.


All we can really say about these products is that given their lab tested plant available Si (using the 5-day method), any grower who purchases either of these products as a source of Si for hydroponic growing is paying far too much for far too little.


Let me demonstrate – the chemistry/science…..


Med-Tek Super Silica contains 14.1% PAS, while Power Si contains a fraction of this at 0.88% PAS based on lab testing (see silica product table, 6 down from top re Fertimaster Power Si).


This means that Med-Tek Super Silica contains 141,000 ppm of PAS while Power Si contains 8,800 ppm of PAS or over 16 times less PAS than Med-Tek Super Silica.


Med-Tek Super Silica is supplied direct to the consumer at $40.00 per litre (landed at your door) while you would expect to pay somewhere in the region of $250.00 per litre for Power Si through a hydroponic store. Thus, if we were to equate the cost of each product, through analyzing purchase price versus PAS ppm in solution, this would mean:


Med-Tek Super Silica = 141,000 (ppm PAS) divided by $40.00 (1 litre)  = 0.000283c per ppm PAS


Power Si = 8800 (ppm PAS) divided by $250.00 (1 litre) = 0.028 c per ppm PAS


These equations tell us that Power Si per ppm of plant available Si is 100 times more costly than Med-Tek Super Silica. I.e. 0.000283c (Med-Tek Super Silica cost per ppm of PAS) x 100 = 0.0283c (Power Si cost per ppm of PAS).


This means that 1 litre of Med-Tek Super Silica, based on plant available Si, is 100 times cheaper than Power Si. What this means is that for equivalent PAS ppm in solution you are paying $40.00 for Med-Tek Super Silica (landed at your door) or $4,000.00 for Power Si (not including freight). Yep, that’s 40 bucks versus four grand. Go figure! Cough! Cough!


The next important thing to realize is based on the manufacturers recommended dilution rate, Power Si doesn’t supply nearly enough PAS to solution. For example, ideally you want at least 30 – 40ppm of PAS in solution. However, based on the recommended usage rate of 3ml/5 gallon, there is 8.8ppm PAS per ml of Power Si = 3 ml x 8.8 ppm = 26.4 ppm applied to 3.785 litres (1 US gallon) = 6.9 ppm per US gallon divided by 5 (gallons) = 1.3 ppm of PAS. That’s 1.3 ppm of PAS or next to nothing, and frankly applying 1.3ppm of plant available Si to solution is almost pointless.  For example, your average river water contains 4 ppm or more (generally >10 ppm) of Si. Basically, you could use river water for free to get more ppm of Si than you would when using this $250.00 per litre silica additive at its recommended dilution rate.


Comparatively, it is recommended that Med-Tek Super Silica is used at 3ml per10 litres. There is 141ppm PAS per ml of Med-Tek Super Silica. 3ml to 10 litres = 141 x 3 = 423 divided by 10 = 42.3 ppm PAS per litre of nutrient solution.


That’s 42.3 ppm of PAS (Med-Tek Super Silica) versus 1.3 ppm of PAS (Power Si).


I could go into the nonsensical, science defying dribble being used to market these claimed to be stabilized silica products but why bother? If the numbers haven’t painted a very clear picture by now, nothing will. For what’s it worth if you are looking to supply silica to plants there are far better options than these overpriced, much hyped, claimed to be stabilized silica products that in actuality provide bugger all silica. That simple!!


Moving on …….


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