How to make your own stabilized mono-silicic acid for use in hydroponics

Mono-silicic acid 3D model
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During the past several years, there have been a lot of “mono-silicic acid” products being marketed for their use in hydroponic culture. These differ from the traditional potassium silicate based products in that they are very acidic in their concentrated form and are stable in solution for longer periods of time at the pH values used in hydroponics. While a hydroponic nutrient solution that has potassium silicate added to it and the pH adjusted to 5.5-6.5 will generally see extensive polymerization of the silicon-containing molecules within 24 hours, these stabilized mono-silicic acid products will be stable for far longer periods of time. They are therefore ideal for use in recirculating systems, where potassium silicate additions can be less effective.

If you watched my youtube video on silicon in hydroponics, you’ll know that the most common way to produce these stabilized products is quite complicated and involves the use of silicon chloride and very specific reaction conditions. These are unavailable to hydroponic growers, reason why it is not easy to produce a home-made version of choline stabilized ortho-silicic acid (ch-OSA). However, choline is not the only reagent that can be used to stabilize silicic acid in solution, and research in industry has shown us that it is actually possible to form stabilized silicic acid products starting from potassium silicate itself.

Orthosilicic acid - Wikipedia
Model representation of orthosilicic acid, also called mono-silicic acid.

This patent describes how to prepare mono-silicic acid solutions that are stabilized by carnitine and several other additives, in the region from 0.01 to 8% silicic acid by weight. The great thing about this process is that we can start from potassium silicate, which is readily available. The concentration of Si obtained will be significantly lower than what is possible when generating ch-OSA – where solutions can reach 40% mono-silicic acid – but the fact that we can prepare it from readily available materials might compensate for this to some extent. It is also worth noting that this process comes from an unexpired patent, so it should not be used commercially without licensing the technology from the owner of the intellectual property.

Extrapolating from the contents of the patent and the examples given, we can come up with a process to brew our own mono-silicic acid at an 8% concentration. Here are the things you will need:

Note the amazon links below are affiliate links. This means that, if you choose to purchase through these links, I get a commission for your purchase, at no extra cost to you.

  1. Potassium silicate (at least 32% K as K2O)
  2. Carnitine hydrochloride
  3. Phosphoric acid (85%)
  4. Propylene glycol
  5. Distilled water
  6. Scale to weight the materials (precision of at least +/- 0.1g, max at least 500g)

To prepare around 425g of stabilized mono-silicic acid, you could follow this process.

Before continuing please make sure you understand what you’re doing. Wear adequate eye and body protection, carry this out in a place with enough ventilation and make sure you read the material safety data sheet (MSDS) of all the materials used. These instructions are provided for educational purposes only, follow them at your own risk.

  1. Add 10g of carnitine hydrochloride to a clean 1000mL beaker
  2. Add 65g of distilled water to the mix.
  3. Stir until all the carnitine hydrochloride dissolves
  4. Add 10g of propylene glycol.
  5. Add 240g of 85% phosphoric acid.
  6. Put the mixture on an ice bath with ample ice.
  7. Wait for 15 minutes, so that the mixture cools down.
  8. During the course of an hour, slowly add 125g of potassium silicate to the mixture with constant stirring. Add more ice to the ice bath if needed to keep the solution cool.

After this, you should be left with an acidic, completely translucid, carnitine and propylene glycol stabilized mono-silicic acid solution that should be around 7-8% w/w of Si as elemental Si. If there’s any precipitate in the solution then the stabilization process did not go well and the silicic acid formed polymerized into silica. This solution should then be used at around 1g/gal, which will provide ~18-20ppm of Si as elemental Si in your hydroponic solution. When using this solution,. the silicon present at the pH used in hydroponics should be much more stable than when derived from direct addition of potassium silicate.

If you go through the above process, leave a comment and let us know how it went.

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23 Comments

  • Talip Duman
    March 26, 2021 @ 7:00 am

    Hello from Turkey. All my Respect to ure Work
    Can i use this solution also as a Foliar spray on my Tomatoe Plants .in hydroponic.and if yes wich ratio. İM also courius how it would Work as a plus against fungal and pest problems. İ read before that Silica sprayed as foliar on Tomatoes would protect against pests and other fungual issues. Have a nice day.

    • admin
      March 26, 2021 @ 8:16 am

      Silicic acid applications do not work very well as foliars, root applications work best. You could use this as a foliar, you would need to adjust the pH to make sure it is in the 6-7 range before applications. You can use the same application rate mentioned in the article.

  • Andreas Manns
    July 27, 2021 @ 7:59 am

    Hi we have tried to make this solution, but at then end it precipitate every time we tried it at different application speed. Do you ad the SiK as powder or in a solution ?

    • admin
      July 28, 2021 @ 8:38 am

      There should be no issues adding it like a powder. If you are getting a precipitate it might be that the amount of Si in your potassium silicate is too high, generally, a high K potassium silicate will be needed for this to work well. Not all potassium silicates are created equal, the % of Si and % of K will be different depending on the grade. Let me know the % composition of your K silicate and I’ll let you know if this is high enough. If it is not, you might need to predissolve it and add KOH to have a soluble enough silicate before the addition.

      Also, the instructions above are also for a pretty high concentration silicic acid preparation, which can be more problematic. Go to the patent linked in the blog post and look at the examples for the lower concentration preparations using Sodium silicate, you might have better luck following those first and replacing the sodium silicate with the molar equivalent of your K silicate.

      • Andreas Manns
        July 28, 2021 @ 9:41 am

        I can’t find the link for the patent in your blog.
        We are using pure K2Si2O5 (CAS 1312-76-1). Predisolving doesn’t work, as it’s pretty insoluble in water, we tried to solve it prior as well.

        • admin
          July 29, 2021 @ 9:08 am

          The link is in the blog post, I put it here in case you cannot find it (https://patents.google.com/patent/WO2012035364A1/en). Also, that potassium silicate will not work, you need a high K potassium silicate, which are much more soluble. You need to use a K silicate that is at least 26% K by weight. A commercial, soluble silicate, like AgSil 16H, should work.

        • Fred Mertz
          March 3, 2022 @ 7:04 pm

          You can try using tetraethyl orthosilicat. The heat generated would be much less. You’d barely have to cool the mixture much. Also you wouldn’t be left with the residual Salts and excess heavy metals.

          • admin
            March 4, 2022 @ 9:26 am

            Thanks for commenting. Yes, there are a myriad of better options from a chemical standpoint. Your proposal included. The objective of this post was just to show a route with “readily available” chemicals.

  • Hassan Alzahrani
    July 30, 2021 @ 5:18 pm

    First, thank you for your effort to enrich the hydroponic community. I’m wondering if I can prepare a stock solution of potassium silicate stored in water of ph >11.5 and use it every 2-3 days at a very low quantity in recirculating systems? The reason is that adding potassium silicate as a liquid is much easier to prepare and measure than solid.

    • admin
      July 31, 2021 @ 9:02 am

      In a recirculating system it can be easier to use a media with silicon, like rice hulls, which can supplement and maintain an adequate level of silicon in solution without having to add anything periodically.

  • Devon
    October 16, 2021 @ 2:25 pm

    I mixed Potassium Silicate with Phosphoric Acid GH PH down and it turns into a sulphur smelling gel-isa substance over the course of some shaking.
    I thought I was on to something. Any chance that is enough to form some Silicic Acid?

    • admin
      October 16, 2021 @ 7:12 pm

      Thanks for commenting. No, what you did was just polymerize the potassium silicate to form silica gel, not forming any silicic acid. What you created is not going to be soluble or available to plants. As mentioned in the article, to form a stable concentrated solution of silicic acid, you need stabilizing agents, not just acidify potassium silicate. Molecules of silicic acid need to be stabilized so that they don’t react with one another or they will polymerize and form silica gel, which is what we want to avoid.

  • Ty
    October 30, 2021 @ 10:15 pm

    Will this add phosphorus and potassium to my current nutrient profile when adding this to my existing nutrient solution?

    • admin
      October 31, 2021 @ 10:05 am

      Yes it will add both. You should calculate the contribution and discount that from your intended nutrient addition.

  • Carlos
    November 10, 2021 @ 9:06 pm

    Hi Dr. Fernandez. I have a question: Can I mix this OSA with any fertilizers on my nutritive solution? Any incompatibility? Thanks in advance and grettings from Mexico

    • admin
      November 11, 2021 @ 6:59 am

      You can mix it into the final nutrient solution but you cannot mix it with a concentrated fertilizer solution.

  • vijayakumar
    December 26, 2021 @