Common questions about silicon in nutrient solutions

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Introduction

We know that silicon can be a very beneficial element for many plant species (see some of my previous posts here and here). It mainly enhances disease resistance and increases the structural integrity of plant tissue. Because of these advantages, you will want to add silicon to your nutrient solution. However, there are a lot of misconceptions and questions about the use of Si in plants and the exact form of Si that you should use. In this post I am going to address some of the most common questions about silicon sources and how to use them properly.

Alkali metal silicates are the most common sources of soluble silicon used. They also have the lowest cost by gram of Si.

What sources are available?

To use silicon in nutrient solutions, we will generally have 3 types of sources available.

First, we have basic potassium silicates, which are solids or solutions derived from the reactions of silica with potassium hydroxide. In this category you have popular products like AgSil 16H and liquid concentrates like Growtek Pro-Silicate. These products have a very basic pH.

Second, we have acid stabilized silicon products. These are products like PowerSi Classic and OSA28. These products are always liquids and contain monosilicic acid in an acidic environment, with stabilizing agents added to prevent the polymerization of the monosilicic acid.

Third, we have non-aqueous products with organosilicon reagents, like Grow-Genius. These products do not contain water and are derived from reagents like TEOS (tetraethyl ortho-silicate) and other Si containing compounds, mainly Si containing surfactants. They are not in forms that are plant available but will generate these forms when in contact with water.

Do potassium silicates contain “less available” silicon?

When you dissolve a potassium silicate at high concentration, it forms silicate oligomers. These are large silicon chains that get stabilized in basic solutions because of their high negative charge. This is why you can create highly concentrated potassium silicate solutions in basic pH. As a matter of fact, making the solutions more basic with added potassium hydroxide often enhances the solubility of potassium silicate solids like AgSil16H (see here for a procedure on how to do this). However, when the molar concentration decreases the silicate hydrolyzes into monomeric silicate anions.

Original background image taken from here. To create a monomeric solution you need high pH and low concentration. Then you lower the pH to get to monosilicic acid.

When potassium silicate is diluted in nutrient solutions, this is exactly what happens. The reduction in concentration hydrolyzes the Silicates into monomers. If the solution pH is then lowered, the final form present will be monosilicic acid. If you properly prepare a nutrient solution with potassium silicate, the end form will be monosilicic acid, the form that is mostly available to plants.

It is a misconception that potassium silicates are somehow less “plant available”. They end up producing monosilicic acid and being perfectly available, when used properly.

How do I properly use a potassium silicate?

First, if using a solid, you need to prepare a stock solution no more concentrated than 45g/L. The recommendation with AgSil 16H would be to prepare a stock solution at 15g/gal and then using this solution at a rate of 38mL/gal of final solution (injection rate of 1%). To increase the stability of your AgSil 16H concentrate you can add 1g/gal of KOH. The end addition to your solution will be +9.8ppm of Si as elemental Si and +11.55ppm of K. The KOH addition and low 15g/gal concentration ensures that silicate will already be largely present as monomeric silicate anions.

Second, make sure to add this solution to your water first. If you add this solution after nutrients, the Si will come into contact with Ca and Mg in its concentrated form, which will cause problems with its stability in solution. Add it first, then add your lowest pH fertilizer concentrate, then your Ca containing concentrate, then finally decrease the pH with an acid to the desired level if needed.

This procedure ensures you get a final solution containing monosilicic acid that will be stable. If you increase the Si in the stock solution, change the injection order, or increase the Si in the end solution beyond 20ppm of Si as elemental Si you might end up with precipitated and unavailable Si forms.

Why would you use acid-stabilized Si products?

Acid stabilized silicon sources are not more plant available. However, their starting pH is usually low and their mineral composition can also be minimal (depending on the preparation process). This means they can lower the need for acid additions and can help lower the pH of hard water sources when used. They can also contain stabilizing agents that could be beneficial for plants. However, the exact stabilizers used and the exact mineral composition used will vary substantially by product, since there are a wide array of choices available to manufacturers.

In the end, at the pH where plants are fed, acid stabilized Si and potassium silicate sources generate the exact same monosilicic acid. Plant availability is not an advantage of using this sort of product.

Why would you use non-aqueous Si products?

These products can be much more highly concentrated than either basic silicon or acid stabilized liquid silicon products by mass. This is because they are made from Si forms that are highly stable under water-free conditions. This means you can buy a small amount and add a small amount to your reservoir per gallon of solution prepared. Another advantage is that they are pH neutral and do not alter the pH of nutrient solutions at all. The formation of the silicic acid from these products requires only reactions with water, so no mineral addition, stabilizer additions or pH modifications happen.

Reaction of TEOS with water to produce different silicic acids (plus ethanol)

A significant point however is that the reaction of a product like TEOS with water releases other substances into solution. For each 10 ppm of Si as elemental Si that you add from TEOS you will in fact be adding ~66pm of ethanol to your solution. These alcohols can be very detrimental for root and plant growth, reason why the use of these non-aqueous Si products needs to be carefully considered. When using a product containing non-aqueous Si sources, it’s important to consider that these substances can accumulate in your root zone and may cause problems. Which organics are present and whether they will cause problems will depend on the exact formulation. When using these organosilicon sources, passing the nutrient solution through a carbon filter to remove these organics before contact with plant roots would be ideal.

Is the final Si in solution from any product type more stable?

No, all three types of products, when used properly, will end up as stable monosilicic acid in your solution. The stabilizing agents in acid-stabilized products will be so dilute that any additional stabilizing effect will be relatively non-existent. If Si is dilute enough (<20ppm of Si as elemental Si), then it will be stable in solution indefinitely (I measured 5 weeks with no changes in concentration). At higher Si concentration, the Si will tend to polymerize (no matter which source it comes from) which will create problems with stability. To have stable Si in solution make sure that you prepare it properly and that you keep the concentrations low enough.

If they are mostly the same in terms of Si availability, why do I see differences between different products at an equivalent Si application rate?

Despite all of the different Si products leading to the same form of Si in the final solution, acid-stabilized Si products will contain a wide array of additional substances that are going to be active nutritionally. For example, Boron and Molybdenum are very commonly used stabilizing agents. Products, like PowerSi bloom, also contain “exotic plant extracts” (according to their website). Commonly used stabilizing agents include glycerol, carnitine, choline and sorbitol. All of these could potentially have an effect on the plants at the concentrations added with these products. Some of these stabilizing agents are usually added at 10-50x the amount of Si present by mass, meaning that your Si supplement might be adding way more of these stabilizing agents than what you’re adding in terms of Si.

What product is more cost effective per delivered mole of monosilicic acid?

There is a lot of space in labeling regulations to allow fertilizer manufacturers to trick people into believing a product might be more concentrated or dilute than another. First of all, labeling a product as “% of monosilicic acid” does not mean that the product contains that percentage of monosilicic acid, it means that the product contains Si, such that if that silicon was all converted to mono-silicic acid, it would give that percent. The only products that contain monosilicic acid in its actual form from the start are acid-stabilized Si containing products, which are usually limited to low concentrations due to the reactivity of this molecule when present.

Both non-aqueous silicon products and soluble potassium silicate products contain precursors to monosilicic acid. One in the form of organosilicon compounds and the other in the form of silicate chains. As mentioned above, both precursors can lead to very high conversions to mono-silicic acid when properly used.

These prices were the lowest prices I could find for each product in Feb 2023. To find current prices, I suggest searching any products you’re interested in. Composition values taken are those provided by the manufacturer, converted to Si as elemental Si. Prices do not include shipping.

To compare the actual concentration of products, it is best to always convert the amounts to elemental Si percentage values. To convert monosilicic acid % values to Si, multiply the value by 0.2922, to convert SiO2 values to Si, multiply the value by 0.4674. For example, 40% Si as monosilicic acid is equivalent to 11.68% Si as elemental Si. Soluble potassium silicates like AgSil 16H can be around ~24% Si as elemental Si by mass, making them the most highly concentrated and lowest cost form of bioavailable silicon when used properly. More highly soluble potassium silicates than AgSil16H will usually be lower in Si, as higher K proportions lead to better solubility and a lesser need to add KOH when preparing stock solution. The table above, showcases the price differences per gram of Silicon of different products as of Jan 2023. When purchased in bulk (50 lbs) AgSil16H can be up to two orders of magnitude lower cost than other alternatives.

I have done lab tests measuring molybdenum reactive Si that show all the Si in AgSil16H can be quantitatively converted to monosilicic acid when following the preparation guidelines mentioned in this post.

What is your recommendation?

After studying the subject for years, using different products with different growers and testing the chemistry myself (preparing stabilized silicic acids and measuring active Si concentrations). Given the price of Si products and the chemistry involved, I would suggest anyone interested in Si supplementation in nutrient solutions to use a potassium silicate solid product. I would suggest to prepare a suitable stock with potassium silicate and potassium hydroxide to increase pH and stability and then prepare their nutrient solutions from dilutions of this stock. If a solid product like AgSil 16H is not available, then using a basic silicate concentrate product would be the next best choice. Usually preparing a more dilute stock from these products is recommended to ensure the stock already contains monomeric silicate.

I don’t think acid-stabilized silicon products or non-aqueous Si products are worth the price premium. If you’re having better results with a non-potassium silicate product compared to potassium silicate, bear in mind that this is likely because either the potassium silicate stock preparation and dilution were not done correctly or the product you’re using contains a substance different from Si that is giving you those effects. The stabilizing agents themselves are going to be much lower cost, so testing the eliciting effects of these agents might be more economical for you than using these expensive products long term.

In cases where mixing stocks and handling basic reagents is problematic or there is limited availability to adjust pH, then the use of non-aqueous Silicon reagents might be desirable. Non-aqueous silicon forms are also the most robust to mixing errors – wrong mixing order, mixing at variable pH, etc – because the hydrolysis reactions happen readily under a wide variety of conditions. However, my recommendation is to always couple these with carbon filtration to avoid potential issues from their organic side-products.

If you have issues with the use of soluble silicon sources – because of your initial water composition, injector limitations, cost, etc – and your media supports amending, I would also suggest considering using solid amendments to supplement Si (watch this video I made for more information). Amending can be a great choice, much more economical than soluble Si supplementation.

Do you have any questions about Si in nutrient solutions not addressed above? Feel free to leave a comment and I might also add it to the post!

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50 Comments

  • Lance
    March 19, 2023 @ 6:35 pm

    Great write up! I like how you addressed making a weaker stock solution so when diluted the initial working solution pH is increased while a limited amount of Si is added.

    But, your following statement is confusing:

    “First, if using a solid, you need to prepare a stock solution no more concentrated than 45g/L. The recommendation with AgSil 16H would be to prepare a stock solution at 15g/gal[.]”

    15g/gal = 56.78g/L =/= 45g/L

    • admin
      March 20, 2023 @ 6:51 am

      1 gal = 3.785L

      15g/gal = 3.96g/L

      45g/L = 170.34g/gal

      Note the 45g is just a max threshold, ideally you would use much more dilute solutions to avoid problems.

  • Moe.Red
    April 20, 2023 @ 3:57 pm

    When a potassium silicate product is used as a buffer, does any part of the potassium become plant available and changes the NPK ratio of the nutrients used?

    • admin
      April 21, 2023 @ 2:59 am

      Yes, all the potassium from a potassium silicate added to a nutrient solution will be plant available and needs to be taken into account in a formulation.

  • Casey
    April 24, 2023 @ 12:51 pm

    Assuming I can control the pH appropriately, could I use the stabilized AgSil 16H in my injection fertigation system to fill batch tanks of nutrients? Would I want to put the AgSil at the front of the injection line? Love the site!

    • admin
      April 25, 2023 @ 4:16 am

      Yes you can, AgSil 16H injections should always be done first, followed by ideally a mixing chamber, then the S/P containing solution and finally the Ca containing solution and any additional pH down required.

  • Valdemar Lunardello Junior
    May 9, 2023 @ 10:28 pm

    Hi professor , I’m using potassium silicate as PH Up to my solution GH Armor Si, because my bloom formula tends to drift down the Ph of my Rez, but I’m in Brazil and the price is very expensive, I have a cheaper option here called (Flex SilΓ­cio) their label says 12%K2O and 12%Si (165,60g/L) of each. The manufacture only recommend to use as foliar spray. Do you think is ok to use as PH Up or should I diluted ? I was thinking in diluted to 4% to became something more close to GH Armor Si, I think the GroTek prosilicate you mention here also has the same 4% K20. So if I dilute , Do I need to use for example potassium hydroxide to keep his PH high? I would like to know your thoughts about and I’ll really appreciate your help ! Anyways, another great topic, thank you !

  • John
    June 2, 2023 @ 8:18 pm

    Can a diluted mix of potassium silicate be dosed into to a batch tank that is constantly being topped up with water and dosed with A and B nutrients? Also pH dosed with Phosphoric acid.
    Basically adding to a nutrient mix of around 2 to 3 EC.

    • admin
      June 3, 2023 @ 2:26 am

      No, the potassium silicate needs to go into water that has a basic pH. If it goes directly into a hydroponic solution it is likely to polymerize. To add to your batch tank prepare the nutrients separately following the correct order of addition and then add the finished nutrients to your batch tank.

      • John
        June 6, 2023 @ 8:28 am

        Thanks for the reply. Sorry, when I said Potassium Silicate I meant to say a liquid version. If I was to dilute for example 5 litres into 200 litres of plain water then dose that into a nutrient mix would it still polymerize? I mean what’s the minimum dilution before it can be added to an existing nutrient tank. Thanks again.

        • admin
          June 6, 2023 @ 9:16 am

          You cannot add a dilute liquid silicate into an already prepared nutrient tank. A silicate going directly into a low pH solution (5-6) will almost certainly polymerize rather quickly, unless the concentration is very very dilute.

          • eduardo
            November 21, 2024 @ 11:10 am

            Hi,

            What would be the ideal ph of initial water to add potassium silicate?

            my guess from your answer is above 6?

            thanks

          • admin
            November 25, 2024 @ 1:39 pm

            Depends on the buffering capacity of the water. If it is RO water, then the pH is irrelevant.

  • TRS
    June 15, 2023 @ 12:48 am

    Fantastic article and great work on this. Something I don’t fully understand is how to compare between liquid and dry Silica products – in your conversion table you calculate to grams of elemental Si per $, but for the liquid products, why would the density of elemental Si be equal to 1 g/mL?

    • admin
      June 15, 2023 @ 5:16 am

      For the liquid products, I am using their w/v% Si values to calculate how much Si they provide. The density of the products is not required for this calculation.

  • Brian
    July 20, 2023 @ 9:12 am

    Can a hydrated food grade bentonite be used as a silicon and potassium addition to hydro or will there be a negative ion exchange with the nutrients? TIA

    • admin
      July 20, 2023 @ 10:52 am

      This won’t work, bentonite does not provide any bioavailable silicon. The silicon in bentonite is completely unavailable to plants and won’t dissolve in any appreciable manner through a plant’s life cycle.

  • Benjamin
    October 6, 2023 @ 11:59 pm

    Thanks so much for your multiple posts on Silicon! Very helpful

    Our system is usually running too high on potassium, but I want to use the cheapest source of Si, which is potassium silicate. Adding potassium hydroxide makes it worse, though not much 9.8g Si to 10g K vs with KOH. 9.8g Si to 11.55g K . Anyway, probably not too much of a difference, but what about using ammonium hydroxide (common “ammonia cleaner”) instead of potassium hydroxide? Also, when the ammonium hydroxide is nitrified, it will lower the pH…possibly offsetting the pH increase from potassium silicate (I don’t know how to calculate the ratio of ammonium hydroxide to potassium silicate need to make it pH neutral after nitrification)

    I think I read somewhere that optimal silica levels are 50-75ppm in nutrient solution, which is 23-35ppm silicon…but seems like you recommend 20ppm of silicon for the reason that you won’t precipitate much. Thoughts?

    Thank you!

  • DJ
    October 25, 2023 @ 2:06 pm

    I’ve been using potassium silicate on my first Dosatron, but calcium nitrate is the next in line followed by the sulfates.. I noticed you said the sulfate should come after the silicate followed by the calcium on the last (or ph down if required). What exactly happens in my scenario where the calcium injector is 2nd in line and not 3rd? Should I switch things around?

    • admin
      October 26, 2023 @ 8:53 am

      You should change the order and make sure the pH is below 6.5 before it gets to the Ca injector, otherwise you will see Calcium silicate precipitates forming with time.

  • Sean
    November 16, 2023 @ 10:24 am

    Having the hardest time with potassium silicate.
    We create stock solutions but at much higher concentrations.
    Should I back that down to your recommended 15/g?

    I was making stock tanks at 500g/g
    Using solution at 1.5 mls/g

    Do you think I would benefit from lowering that concentration as it’s probably polymerizing.
    Would love a conversation about this πŸ™ I moved away from power si, I felt like I was getting ripped off.

    • admin
      November 16, 2023 @ 12:52 pm

      Thanks for writing. Injecting potassium silicate from highly concentrated stocks can cause problems because the silicate goes into dilution from oligomers and not from monomers, if this process happens too quickly it will all be unavailable in solution and will fall out much more easily. Using highly concentrated silicate solutions requires using much higher pH. My recommendation would be to lower your injection to 1:100 and keep your Agsil 16H rates below the ones mentioned in the post, also make sure to add KOH to increase the pH of the mix to increase stability as explained in the post as well.

      If you need any further assistance, I would recommend to book an hour of consulting through my website (http://scienceinhydroponics.com/book-now)

  • Alison
    December 2, 2023 @ 9:38 pm

    Great write up! (Hopefully) quick question: in terms of basic basic potassium silicate products and acid stabilized ones, some people say it’s a good idea to wait 20 minutes to 24 hours after adding the silica product to the water and before adding fertilizer products. Most manufacturers of these products I’ve come across do not call for this wait time in their instructions and FAQs. How necessary is it to wait in your experience? Does it make that big of a difference?

    • admin
      December 3, 2023 @ 11:19 am

      Thanks for commenting. There’s no need to wait beyond what it takes for dilution to happen, which should be quick. Waiting will only enhance the chances of polymerization happening, so fertilizer should be added after silicate addition as soon as dilution is complete. Monosilicic acid at a concentration of ~10-20 ppm of Si as elemental Si is stable almost indefinitely in solution but larger concentrations will start polymerizing rather quickly.

      • Dayowe
        December 10, 2023 @ 5:43 am

        Thanks for addressing this I also frequently see people recommend to mix in Silica first and wait for at least one hour of mixing before adding other things. Where is this sentiment coming from, or better: what forms of Silicon forms does it apply to?

        Also, in your response to Alison you say “fertilizer should be added after silicate addition as soon as dilution is complete”. I assume before adding fertilizer we’re bringing the ph down to below 6.5? Or is this step only necessary if the pH is not yet below 6.5 after adding the base nutrients and before adding Ca containing solution? E.g. my base nutrients would bring the pH down to below 6.5 pH, but when I did this i had a lot of translucent/white, slimy, floating things in my res, which I assumed was precipitates from incorrectly mixing.

        I currently am using Grotek Pro Silicate and mix this into RO water. My takeaway from your response is that I should in the future add my Potassium Silicate first, wait for dilution to complete, then bring pH down to below 6.5, then add Base nutrients, then my Ca(NO₃)β‚‚ stock. Is this correct?

        Do I at any point in this process need to wait a longer time before adding anything, e.g. after bringing the pH down subsequent to adding the Potassium Silicate? from what I learned from reading your blog, bringing down the pH after this converts the Potassium Silicate into monosilicic acid. Do i need to give time for this process to complete or is it pretty immediate?

        Thanks for sharing your work in your blog! I love coming back to your posts and reading new content!

  • Corey
    December 4, 2023 @ 2:06 pm

    I currently add Grotek-Gro silic to my water which starts at 0ppm. After the monosylicic acid is added my water and silicone mixture reads (0.4 EC) – 20ppm using a Hanna TDS meter set to the 500 conversion.

    Does this mean I am adding 20ppm of Elemental Si – as a generally accepted range, or am I adding 20ppm of monosylicic acid Si(OH)4 ?

    If it is 20ppm of the monosylicic acid , how do I convert the value , so I can estimate how much actual elemental Si I am adding when using this meter reading ?

    Cheers

    • admin
      December 4, 2023 @ 3:01 pm

      Thanks for writing. Neither is correct. The ppm from your meter is not the ppm of Si or monosilicic acid, in fact it is not the ppm of anything in solution. If you’re on the 500 conversion this just means that you have a solution of silicate with the same conductivity as a solution that has 20ppm of NaCl. The TDS measurement tells you that your solution is as conductive as some ppm concentration of a standard pattern (this is why there are several scales, depending on which pattern). To measure Si you need a lab analysis or a colorimetric test kit that can do specific Si detection.

  • Corey
    December 4, 2023 @ 5:04 pm

    Is there some math involved where you can equate the molar mass and ppm of NaCl and convert it to Si?

    When the Grotek bottle suggests 0.6-1.2ml/ gal are we to assume it’s in a 20-50ppm range ?

    I’m guessing many website forums where semi pro growers say their ppm is 40ppm of Silicone after adding to water, they are just stating their tds meter which as you’ve shared is not correct.

    I found this kit that can do 1-75ppm. Many of the cheaper ones only do 1-10ppm. Do you recommend a particular kit ?

    https://www.coleparmer.ca/i/hach-24296-00-colorimeter-test-kit-silica-0-to-75-ppm-100-kit/9957419

    • admin
      December 5, 2023 @ 5:39 am

      There is no way to easily translate these numbers, you would need to create your own calibration curves to create an equivalency. Also bear in mind that the monosilicic acid is not conductive (it is a neutral molecule), so it will not register in a conductivity meter at all. Conductivity is not a good way to quantify silicon compounds in solution.

      When growers say they are using 40 ppm of Si, they are likely just making a calculation from the composition of the Si source they are using and assuming those are accurate. They are likely not taking this reading from any TDS or Si specific measuring kit, but just doing the calculation based on the initial concentration of the source and their rate of addition. They are therefore assuming there is no Si loss, the composition cited by the source is accurate and the addition amounts are measured accurately. If anyone is using a TDS meter to add any ppm of Si, then they are doing it incorrectly.

      You can calculate how many ppm of Si you can expect from an Si source by using the Si % composition of the source and your rate of addition in mL/gal or g/gal.

      An Si measuring kit would be more accurate in that you would know how much Si you actually have in your water. The coleparmer kit you cite would be adequate. However make sure to use it before adding any Fe or P to the solution as those would interfere with the kit. However, unless you’re doing some research, this is not needed to successfully use Si in cultivation, just calculating your expected Si ppm addition and adding the relevant amount is accurate enough.

  • Corey
    December 8, 2023 @ 4:00 am

    Thanks again for sharing more insight into how silicone in a fertilizer solution works.

    I created a formula I’d like to share which will calculate how much Silica product to add when you have a target ppm in a set amount of water volume.

    S𝑖 π‘π‘Ÿπ‘œπ‘‘π‘’π‘π‘‘ (π‘šπ‘™) to add = (π·π‘’π‘ π‘–π‘Ÿπ‘’π‘‘ π‘π‘π‘š βˆ— π·π‘’π‘ π‘–π‘Ÿπ‘’π‘‘ π‘‰π‘œπ‘™π‘’π‘šπ‘’ π‘Šπ‘Žπ‘‘π‘’π‘Ÿ(π‘šπ‘™)) / ((10^6 βˆ— 𝑆𝑖%) βˆ’ (π·π‘’π‘ π‘–π‘Ÿπ‘’π‘‘ π‘π‘π‘š βˆ— 𝑆𝑖%))

    • admin
      December 8, 2023 @ 11:40 am

      Thanks for sharing. However, this formula is not correct. Pay attention to your unit analysis, your units are not correct. The final ppm of Si from a product addition is determined by this formula:

      Si as elemental Si ppm = (Vol_addition in mL * (0.001 L/mL) * Si as elemental Si% * (10000 ppm/%)) / Final volume of solution in L

      To calculate how much volume to add you can modify the equation:

      Vol_addition in mL = (Si as elemental Si ppm * Final volume of solution in L) / ((0.001 L/mL) * Si as elemental Si% * (10000 ppm/%))

  • Corey
    December 8, 2023 @ 11:46 pm

    Thanks for reviewing my formula but I don’t understand yours. Using my formula if I wanted to use Dynagro Protek which is 0.078 % Si , and if I wanted 20ppm of that Si in 1000 ml of water, my formula would suggest to add 0.26ml of Protek. I don’t understand the need for the 0.001L/ml or the 10,000 ppm / % ? Could you use my numbers of 0.078 & 1000 ml in your formula so I might understand it better ?

    • admin
      December 9, 2023 @ 5:25 am

      The product you mention is NOT 0.078% Si, it is 7.8% Si as SiO2 (per the label). This means that it is 3.64% of Si as elemental Si. For this product, with a target of 20ppm of Si as elemental Si in a final volume of 1L, the results would then be:

      Vol_addition in mL = (20 ppm * 1L) / ((0.001 L/mL) * 3.64% * (10000 ppm/%))

      Vol_addition in mL = 0.55mL

      This is correct because 0.55mL at 3.64% Si as elemental Si would contain 0.020g of Si, which when dissolved in a final volume of 1L would give 20ppm of Si. Be very careful when reading labels because Si as SiO2 or Si as Si(OH)4 need to be converted to elemental Si for these calculations. Also the 0.001L/ml and 10,000 ppm/% are used for unit conversions, to arrive at the proper units in the end. This is why I mentioned you need to pay close attention to your unit analysis, you need to make sure your equations always produce the right units and that the conversion factors always contain the proper units in them.

      If you have additional questions I would recommend booking an hour of consulting so that I can help you clear all your doubts on the subject.

      • Corey
        December 9, 2023 @ 12:08 pm

        Thank you for your explanation. You have been very generous. I’ve noticed Protekt has a number of label versions floating around the internet. Some say 7.8% Si, some say 7.8% Sio2, some say 7.8% as soluble Si , some new iobes are even saying 3% Si.

  • Mark
    December 22, 2023 @ 8:59 am

    hello,

    Is it fine to adjust the pH(add acid) right after add potassium silicate?

    I always adjust the pH first and then mix the nutrient solution.

    • admin
      January 12, 2024 @ 4:20 am

      From a chemical perspective that is perfectly fine provided you ensure the Si is fully mixed.

  • Nick
    March 24, 2024 @ 5:54 pm

    I have one main RO reservoir that I am looking to buffer. That reservoir then feeds a set of holding tanks. Those holding tanks are hooked up to the dosing skid which mixes the nutrient concentrate directly into the holding tank.

    My concern is this: The RO reservoir mixes the treated water into the holding tanks which is controlled via a float. When the level drops enough the holding tank automatically fills. If I mix the potassium silicate into my RO reservoir beforehand, and then that water mixes into my holding tank which already has feed in it, could that cause a reaction/precipitate?

  • Nick
    June 11, 2024 @ 12:37 pm

    Hi

    Just wondering if I were to use potassium silicate as a foliar, would it be plant available or should I purchase an acid stabilised silicic acid?

    Kind of curious, would the leaf take up the silicate and then make the conversion to silicic acid? The current product I have is coupled with humic acid and kelp, so thinking the leaf should absorb it…

    Kind Regards

    Nick

    • admin
      June 14, 2024 @ 10:36 am

      Thanks for writing. Uptake of silicic acid through leaves is quite limited – leaves are not roots and silicic acid is quite unstable – the silicon basically deposits on the leaf surfaces it interacts with. This can help to with things like preventing PM, but you will need to spray frequently as new tissue that grows will not contain any silicon. It is much more effective to apply this through the root zone, where it is evenly distributed throughout the plant through the xylem. Studies have shown consistently that root applications are much more effective compared with foliar applications (see my blog posts on Si). Keep your kelp in the foliar and your Si in the root zone.

  • Dave
    June 27, 2024 @ 10:03 pm

    Thank you for this write up, it’s been very illuminating.

    In recirculating hydroponics (assuming that a consistent elemental Si concentration of 20 PPM is ideal to balance benefit and solubility), silicon is a bit of a conundrum. Would you suggest treating a fresh reservoir with a basic potassium silicate based product to maximize the economics and then continue to add a trustworthy stabilized silicon product for the remainder of the tank life?

    Are there any rules of thumb when it comes to silicon uptake by plants and how quickly or slowly this occurs? Thinking about how to adjust re-addition rates without colormetric analysis of the water on a regular basis.

    Thanks!

  • Dave
    June 27, 2024 @ 10:07 pm

    Great Article thank you!

    For recirculating hydroponics would you suggest starting with a potassium silicate based product (like AgSil) for the initial fresh tank and then add back a stabilized over the remaining course of the tank life?

    Are there any rules of thumb on how quickly or slowly silicon is removed from solution that we can use to estimate the rate at which to add back Si to the tank?

    • admin
      June 28, 2024 @ 8:25 am

      Thanks for writing. The rate of removal depends fundamentally on the rate of transpiration. You can add silicon from AgSil periodically, to replace what has been lost. As a rule of thumb you can replace the initial amount every time you replace the initial volume of water 3 times. Do not add Agsil directly into the tank, but dilute and adjust pH before adding to the main system.

  • Sam Johnson
    June 30, 2024 @ 2:16 pm

    Thank you very much for this great article.

    Would be awesome if you would answer my question.

    Do I need to use potasium hydroxide or can I use any other acid?

    My ph down solution is made of citric acid which is not so stable (Biobizz PH dowm).

    Thank you so much

    • admin
      July 1, 2024 @ 8:48 am

      Thanks for writing. Potassium hydroxide is a base, not an acid. It cannot be replaced with an acid.

  • Dante
    July 3, 2024 @ 9:50 am

    Hola Daniel, podemos usar este silicado de potasio k-40? https://www.mejorsil.com.ar/
    Para preparar concentrado de 10%SiO2, viene en formato liquido

    • admin
      July 10, 2024 @ 8:12 am

      Gracias por tu comentario. Tendria que ver los anΓ‘lisis para decirte con seguridad, pero probablemente si lo puedes usar.

  • David
    July 30, 2024 @ 12:29 pm

    Hello Dr. Fernandez,

    Thank you for this excellent article.

    In reading through this article several times I have a follow up question regarding the graph in the first section. There appears to be a floor concentration (somewhere between 0.001-0.0015 mol/kg) at which elemental Si is primarily in the monosilicic acid form regardless of pH (although the graph does not go below 5). When I do the math on elemental Si in PPM at that molar concentration I get ~28 PPM at 0.001 mol/kg. (0.001mol/kg *28.08*1000=~28 PPM) Is this accurate?

    If that is correct, does it then follow that a silicate solution with elemental Si of 28 PPM (conservatively) or lower can be added to a solution with low pH without risk of precipitation? I have seen multiple comments above stating this is not the case so I am wondering if there is something key I’m misinterpreting.

    Thank you,
    David

  • Yet another David
    November 12, 2024 @ 5:37 pm

    So from my understanding of reading through the comment section, if using a recirculating system, and consistently topping up by hand 2x daily, what I would need to do is:

    Create a AgSil 16H + KOH stock solution at provided rates.
    Dilute Silica stock solution into “Top-up” water, and adjust pH to 6~
    Add this to reservoir, then proceed to add Organic Acids (Fulvic/Hummic), then B, and finally A?

    If the Silica solution has already been pH adjusted to normal Hydroponic values, does it still specifically matter the order in which Nutrient stock solution is added to the final solution, or is adding Sulphates/Phosphates (B) first just a matter of precaution to protect from pH swings to help prevent the precipitation of Si?

    Or would you prefer only adding Silica back into the system on something like a weekly basis (8 gallon reservoir, losing 3-4 gallons daily)?

  • Enete
    May 23, 2025 @ 11:32 am

    How I miss chemistry classes! lol

    Well… I would like to summarize and confirm a little of everything I read about application in fertigation without tanks, just preparing fresh solutions manually.

    The product I have available at my garden center is potassium silicate, whose label reads:

    Guarantees:
    Silicon (Si) = 12%
    Potassium (K20) = 12%
    Density = 1.43
    Raw Materials: Potassium Silicate Solution.

    To obtain 20ppm of elemental Si in the final solution:

    – Add 0.154 ml of my Potassium Silicate solution to 1l of RO water.
    – Acidify the solution made with phosphoric acid to the target pH~6.5
    – Add a base fertilizer solution
    – Check if the pH is not above 6.5 (it probably won’t be, but if it is, should I acidify it to prepare it for the next step?)
    – Add a fertilizer solution containing calcium [Ca(NO₃)β‚‚]
    – Adjust the pH of the final solution to the desired level

    Thanks in advance for your contributions!

  • Andy
    July 11, 2025 @ 11:52 am

    Thank you for the wealth of top-quality knowledge you generously provide with this blog.

    If I am using an (Agsil16h stock solution) + (Part A) + (CalNit) regimen in alignment with your recommended mixing order, do you have a recommendation for when to add a fulvic acid product as a chelating agent, if at all?

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