Let’s talk silica

its still legal on the non cannabis market= pacy is under 200 per gal. I dont think i need it.

I apologize for the slow reply @emdub27.

Thanks for the vote of confidence, but I know enough about silicate chemistry to know there’s more I don’t know than I do know :wink:

Therefore, to get you the most accurate answer, I contacted Steve Fickett of Thornton Laboratories Testing and Inspection Services. Thornton Labs was fundamental in developing the only soluble silicate analytical method for non-liquid silicate products accepted by the Association of Official Agricultural Chemists (AOAC International). In fact, his partner Hugh Rodrigues was the co-author, and Dennis Sebastian of Thornton Labs was the primary author of that seminal work: A 5-Day Method for Determination of Soluble Silicon Concentrations in Nonliquid Fertilizer Materials Using a Sodium Carbonate-Ammonium Nitrate Extractant Followed by Visible Spectroscopy with Heteropoly Blue Analysis: Single-Laboratory Validation

Steve was unsure of the answer when I called him. He asked me to email him the question so he can run it by Hugh Rodrigues. I’m also going to run the question by Dr. Daniel Fernandez.

In pure water without acids (excluding carbonic acid), greater than about 80% of the silicon (Si) from potassium silicate (like AgSil 16H) should be in the form of othrosilicate (at the working range you posted). Based on the fact the silicon in potassium silicate like AgSil 16H has a SiO2:K2O ratio of 1:1.6, with higher solubility than sodium silicate at a 1:2 ratio of SiO2:Na2O:

Once acidified, I would estimate greater than 90% of the orthosilicate converts to orthosilicic acid. So, overall, for a ballpark answer to your question, I’d guess greater than 70%. However, that figure could be lower considering you’re using organic acids rather than solely using mineral acids. And that’s assuming the calcium concentration isn’t too great to affect silicon solubility.

I will have data to share once I send in samples of my stabilized orthosilicic acid solution to be tested by Thorton Labs. Comparing thier quantifiaction of orthosilicic acid in solution to my calculation of 4% and 6% orthosilicic acid (assuming 100% of the silciate from AgSil 16H becomes orthosilicate into orthosilicic acid). The test is $85 and takes five days, so I should have data to share the week after next.

This document from PQ Corp may interest you: Sodium and Potassium Silicates: Versatile compounds for your applications


@Flowerman thank you very much for the detailed reply.

The main reason I asked the question is because when I augment my existing nutrient solution containing agsil 16h with power si I see an obvious difference, mainly in resin production. If I augment the same solution with agricultural grade silicic acid products from Loveland, or Rexil I see no difference.

I don’t know if I should assume that Loveland and Rexil are just selling potassium silicate or assume that there is something in power si in addition to silicic acid. Maybe power si is the only company that has figured out how to keep the silicic bioavailable in solution.

Sap and tissue analysis were run on both crops, power si improved overall nutrient absorption. there were no obvious differences in nutrient ratios or any deficiency such as boron being corrected by power si .


The difference, I suspect, is that Power SI is stabilized orthosilicic acid. Because orhtosilicic acid is unstable, so once it’s formed it will convert back to silicon dixoide or other speices, even if you keep pH very low. The other ions and the organic acids in your solution will reduce its stability even further.

The other silicate products you mention don’t provide stabilzied orthosilcic acid. So, a better comparision would be to use e.g., Fasilitor (or other stabilizied orthosilicic acid products) at the same concentration as you’re using Power Si. That way it’s an apples to apples comparison, instead of apples to oranges.

Heck, I’d be happy to send you my stabilizied orthosilicic acid formulation to run against Power Si:


I don’t normally run power si. I have one client that swears by it, and that caused me to do a couple of test benches at one of my facilities. The Rexil product is AB Yellow and is advertised as a stabilized silicic product. The Loveland sst product is also advertised as stabilized.

With my background (horticulturalist) I just find it hard to believe that no actual stabilized silicic is available to commercial ag producers. I also inherently distrust anything sold in a hydro store due to the cat and mouse games the nutrient companies play adding off label ingredients to many products. We’ve tested a few and found everything from synthetic cytokinins, auxins, jasmonates and salicylic acid to every giberrelin inhibitor you can imagine.

When supplies arrive I will be attempting to make the sop you posted above.


Thanks for that. I didn’t know they were stabilized orthosilicic acid. Considering what you wrote, a few things come to mind:

  1. The product formulation dictates the degree of stability once diluted into a working solution. For example, the formulation I shared is considerably more stable than the most commonly used choline chloride stabilized products (like Power SI, I assume). I would also assume Rexil and Loveland SST are choline chloride stabilized. There are only a few manufacturers in the world who make stabizlied orthosilicic acid. Those mfgs then white label for other companies (contract manufacturing).

  2. In the cannabis world, many companies provide considerably more a.i. than listed on the label. I’d have Power Si analyzed by Thornton Labs to see if its orthosilicic acid concentration (a.i.) is greater than listed on the label.

  3. You make an excellent point about non-listed a.i. Normally pesticides (as defined by EPA), commonly called plant growth regulators. I wouldn’t put it past Power Si to include them. However, due to the complexity of silicate chemistry, I would guess they don’t. Testing is critical like you wrote, if you suspect unlisted PGRs.

  4. Stabilized orthosilicic acid products are common in AG in Europe (Spain comes to mind) and elsewhere. But not in the US. And they are most commonly applied as foliar sprays, not drenches. I would consider Loveland to be AG.

Also, I agree about grow store nutrients (or any nutrients marketed to cannabis). I formulate and mix all my nutrients, supplements, PGRs, and surfactants/adjuvants (except for organosilicate). I’m a plant biologist.


I specifically chose to try Rexil AB Yellow because it is used in quite a few studies that showed profound results. It is advertised to be peg-400 stabilized. I lack the chemistry knowledge to know how that would compare to choline.

Since you already have a relationship with Thornton and plan on sending your sample to be analyzed would you be willing to send a sample of power si along with it? I’ll pay for the power si and the testing for it as long as we can share the results with the community.

I also agree that Loveland as well as Rexil are ag grade products. What provoked my original question was that I did not get comparable results to power si using either of these ag grade products. Results also were not statistically different than what I typically see using agsil 16h. I began to question if my low ph (because I hate having to flush drip lines) was in fact making the silicate in my solution more bioavailable. At the same time the pH of my medium is pretty much average, stays around 5.9 due to the weak acids and an all nitrate nitrogen supply.


Your posts triggered my memory about ReXil…

AB Yellow by ReXil, formally SiLife BV, used to be known as OSAB3 under SiLife BV. In ReXil AB Yellow, the PEG-400 functions as a humectant to retain water and prevent polymerization (gelling), stabilizing the orthosilicic acid. And boron is used as an auxiliary stabilizer, again to prevent polymerization of the orthosilicic acid.

When comparing PEG-400 stabilized H4SiO4 to choline chloride stabilized H4SiO4, it has been reported that PEG isn’t as good as choline (“the standard” from the quote below), in terms of orthosilicic acid stabilization. And both are consideraly worse than using carnitine to stabilize H4SiO4, especially with phosphoric acid for acidification and PG (or glycerol, or PG:glycerol) as a humectant auxillary stabilizer (my SOP):

It was observed that polyethylene glycol (PEG-400) does destabilize H4SiO4, where observed gelling time was more than 30% shorter than that for the standard (Table 3 ; Experiment 5 / Experiment 1 ) .

To compare PEG-400 stabizlied H4SiO4 like Power Si or ReXil AB Yellow, make sure you’re providing the same concentation of H4SiO4. Simialry, to compare Power Si to choline stabizlied H4SiO4 like Yara’s ActiSil (not available in the US?), and to carintine stabilized H4SiO4 (my SOP), make sure you’re providing the same concentration of H4SiO4.

From Silicon in Agriculture (an Ebook worth reading; I had a negligible impact on it after conversing with the author years ago):

Today, stabilized silicic acid (SSA) is available in several liquid formulations for foliar application. The first is SSA in comation [sic] with molybdenum and zinc, the second, with molybdenum, zinc, boron, and copper, stabilized with PEG (polyethylene glycol) available as Siliforce® from Agro-Solutions BV (PT). A second series of formulations consists of OSAB3 (SSA also PEG stabilized, combined with boron and other mineral elements), marketed as SAAT (Silicic Acid Agro Technology) by ReXil Agro BV (PT). Both of these companies also supply other products that stimulate plant growth and are synergic whem [sic] applied together with SSA (e.g. L-amino acids). A third is SSA stabilized by Choline rather than PEG and marketed by Yara, ActiSil (poinsettia white paper).

Disclaimer: The leading Partner companies for this blog are: IGNIBRITE INC, USA; REXIL-AGRO BV, ILSA

Regarding testing of Power Si, I just remembered there’s no need. Brian over at Custom Hydro Nutrients already tested it, as well as SST from Loveland. So, it would be better to get ReXil AB Yellow tested to add to the data set. That way, we have test results for all the major stabilized orthosilicic acid suppliers and the newest state of the art that I used to create my SOP:

If you send me some ReXil AB Yellow, I’ll pay for its testing and share the data here. Also, it would make sense to get each product analyzed for plant nutrients (auxiliary stabilizers) as well (B, Mo, Zn, and Fe). So, if you send me some Power Si, ReXil AB Yellow, and Loveland’s SST, I will have their mineral profiles tested and share those data too.

The testing by Brain at CHN shows that Loveland SST has half the orthisilicic acid (PAS; plant avaiable silicon) as Power Si. I’m not sure if the use rate of SST is twice that of Power Si. If not, that shows Power Si is providing a greater concentration of orthosilicic acid. So this could be why you’re seeing more significant results from Power Si.

Also, from reading the LoveLand SST label and SDS, I have doubts it’s PEG-400 stabilized. What’s the pH of the product?

Normally, a mildly acidic fertigation solution won’t affect soil(less) solution pH. Due to chemistry, including what you described from nitrate (OH- release by roots) and use of weak acids. So the impact of low pH on H4SiO4 present in the soil(less) solution would be negligable. That said, your working solution pH is very low, so maybe there’s something to your hypothesis - assuming your use of organic acids isn’t negatively affecting silicon soulblity. Unless you’re already doing so, it would be interesting to take lysimeter samples to spot test soil(less) solution pH, and use the Pour-Thru method for accruate pH measurement.

Lastly, to avoid the necessity of overly low pH, have you considered using polyphosphate? Not the over-priced and over-hyped hydro store product DripClean (with all its sodium). Rather, the AG product from Haifa: GrowClean (N-P-K; with orthophosphate and polyphosphate). I can confirm that GrowClean works very well to achieve your stated goal. And as a bonus, recent research has found that when polyphosphate comprises 10% to 30% of total phosphate, generative plant growth is improved (through various physiochemical effects, including increased Ca and Mg uptake by roots).

P.S. I too use an all nitrate nitrogen supply thanks to the amazing CalPrime. Ammonium can kick rocks, lol. My solutions only have negligible ammonium.


I like it because it is completely stable until mixed with water.


The only one I currently have on hand is power si. I’ll get sst and Ab yellow coming, I quit keeping them on hand after not seeing results I wanted from them.

Just to make it clear I do not see a profound difference with power si. I’ve ran side by sides with it 3 times as controlled as I can and see no yield change, but a small increase in total cannabinoids. We are talking going from 30% total cannabinoids to 31% total cannabinoids. In my opinion it isn’t worth the added cost of power si over agsil 16h. I was looking for something that would deliver the same results for less money when experimenting with AB yellow and sst.

I have tons of data in my grow. Continual monitoring of pH and ec of feed as well as runoff on 6 distinct zones. Each zone also has 2 grodan grosens to monitor the medium. It is all rockwool at this time because I don’t get to make all the decisions. We average 4.2pH in, 5.9pH on the Grosens, and 6.2pH runoff.

I have not tried haifa grow clean. I run ICL pekacid as a primary phosphorous source. The low feed ph isn’t of concern, it works and by all accounts the weak organic acids are definitely not detrimental. I’ve been running similar mixes for a couple of years. I specifically chose to use weak organic acids knowing that they will not drastically upset anything in the root zone. We do it differently for clients with different mediums and or recirculating systems.


at some point in my Living organic soil journey i thought ai read that silica disrupts the microbes? but im not seeing it when I google it. am i just wrong?

Ah, from your earlier posts, I thought you saw a big difference between Power Si vs. the others. I agree paying those crazy prices isn’t worth it. AgSil 16H is great for the main reason to use Si, for IPM and stress tolerance. Plus, trichomes are highly silicified…

WRT the organic acids, I only meant that they could be affecting the silicon in solution, not the plants or rhizosphere.

I’m interested in what you see after trying the carnitine stabilized orthosilicic acid from my SOP.


We will know soon, the sop specifically calls for glycerol, so I’m waiting on reagent grade glycerol to show up.

I will also try to do a small batch with lower grade vegetable glycerine to see how that works out.


Using glycerol is the better choice, but vegetable glycerine works as well (considering its mostly glycerol). However, for the best stability, PG is the optimal choice as a humectant.

I’ll edit my previous post where I referred to glycerol as glycerin to avoid confusion by other readers. I tend to use the terms interchangeably because I wrote the SOP for user-friendliness.


So in your opinion what is the best silica on the market thats readily available.


Commerical product for root appliction, AgSil 16H. Making sure to keep Si below about 25 mg/L. For DTW soilless cultvaiton about 10-20 mg/L Si, for hydropoincs about 5-15 mg/L.

For stabilized orthosilicic acid of a commerical product, ReXil AB Yellow. Unless Yara has started selling ActiSil in the US. As foilar application (preferred), or root application in hydroponics. But I think the SOP I shared provides a better product and is much cheaper, just need to make it yourself.

The jury is still out if stabilized orthosilicic acid is better than just potassium silicate for root application in soilless substrate (like peat or coco) and inert media (like rockwool), but OSA is probally a better choice for hydropoincs like NFT, aero, and RDWC vs. potassium silicate. I plan to run controlled trials later this year with coco and rockwool using PEG-OSA (ReXil, Power Si, Fasilitor, etc.), ch-OSA (ActiSil, other AG products), carnitine-OSA (my SOP), and AgSil 16H.

Oh yeah, Mills Vitalize is white label of ReXil AB Yellow (according to Mills). Totally forgot that, and it was tested by Custom Hydro Nutrinets. Came in at 0.94% orthosilicic acid, more than Power Si (@0.88% OSA).


What happens if this is exceeded? Just general anion lockout? I assumed the Si would just precipitate out before it was every really a plant toxicity issue.

Also wanted to say your info is informative, well-written, and a pleasure to read. Thank you.


Seriously…Been reading everything @Flowerman and @emdub27 say multiple times, just to make sure it sinks in



Most likely due to the silicate reacting with Ca, forming calcium silicate and precipitating out of solution. It would just be a waste.

You can actually watch this happen in a doser mixing chamber.

In my experience you can get away with a little more by running a quality fulvic product in your calcium nitrate stock tank.


My lazy google math says that CaSiO3 has a solubility of around 100ppm so an Si content of ~15ppm which works out pretty well. Makes me think that as long as the cation doesn’t unduly impact the other nutrients you really can’t have too much