Friday, February 13, 2009

My pH Balancing System for Hydroponic Growing

In the past few days, several people have asked me how to use my carbonate/citrate buffering system as a means to control the pH of their nutrient solutions. For this reason, I decided to write a post which explains the simple way in which my buffering system can be prepared and a little more about how it works and what you can expect from it.

A pH buffer's function is to provide reaction "alternatives" for strong acids and bases when they contact the nutrient solution. These acid or basic substances generally react with water and this changes the value of pH. When a buffer is present, they react with the buffering molecules instead of water. This of course, makes pH remain approximately constant. Since the generation of species can be perfectly controlled and predicted by the use of mathematical methods, we can create very good buffering system by "experimenting" with different substances using a computer, as I mentioned in an earlier post.

As a result of my simulations I concluded that a mixture of citric acid/carbonate acts as a good buffer in hydroponics both towards the addition of acids and bases. The actual species involved are citrate and the bicarbonate ion, the bicarbonate ion reacts with acids, providing basic pH buffering, while the citrate reacts with acids providing an acid range buffering effect.

It is very easy to use this system by using your regular pH meter. Prepare your nutrient solution as usual, at the end, add 5g of citric acid for 500 liters of solution (this will acidify the pH of your solution a lot). Now, take back the pH to the value you want (5.8 to 6.2) by adding potassium carbonate. It is important not to use bicarbonate as this will react quickly with citric acid to form carbonic acid and then carbon dioxide (which will leave as a gas !). Also make sure you add both chemicals previously dissolved in water to afford quick chemical equilibrium achievement inside the solution.

By using this method you will have a nutrient solution that is perfectly buffered at your desired pH and that will remain at that pH value for a good amount of time. This of course, depending on the solution's volume and the type and number of plants you grow with it. (below, the distribution of species diagram or the carbonate family)
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10 comments:

  1. Hi, have you actually tested this in real life or only theory? Sounds very useful if it actually works

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  2. Yes, I have tested this in practice for the past 2 years. I am even working on buffering products based on a similar concept for a US fertilizer company.

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  3. That's great to hear. What other elements do the citric acid or potassium carbonate add to the solution? Do they amount to a significant number of PPM's when the Ph is brought back up to 5.8?

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  4. I've read fom a different user that according to yourself, to quote, "This buffer has several problems, particularly the precipitation of calcium citrate from the nutrient solution. Truth be told, this buffer must be used very carefully and only in very moderate amounts to prevent this from happening."

    What are the other problems it presents and can you suggest a more sparing set of proportions to apply this buffer? Thanks!

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  5. I've read fom a different user that according to yourself, to quote, "This buffer has several problems, particularly the precipitation of calcium citrate from the nutrient solution. Truth be told, this buffer must be used very carefully and only in very moderate amounts to prevent this from happening."

    What are the other problems it presents and can you suggest a more sparing set of proportions to apply this buffer? My reservoir changes will be weekly. Thanks!

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  6. Well thanks a lot for your interest. It is true that calcium citrate precipiation may become problematic when the buffer is abused and care should be taken to keep the buffer at about 1mM concentration to avoid precipitation, as I said, it should be used carefully. A 1mM concentration is enough to provide a very efficient pH buffer and avoid precipitates. Potassium carbonate and citric acid do not add anything detrimental to the solution, the amount of potassium will not be very significant. The increase in conductivity should be around 0.1-0.2 mS/cm, but it is not extremely high. If you are changing your solution weekly then it makes no sense to use a pH buffer, the buffer is designed to maintain constant pH for a couple of months. It is very unecessary to change a reservoir weekly, it is certainly a waste of nutrients. I cannot provide further details into the exact use of this buffer or the solutions to its problems as I would violate my current product development contract and non disclosure agreements. I hope this helps ! :o) Thanks Again for the interest !

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  7. Hi, I'm in Uruguay, and all I can get is Phostrogen Plant Food for nutes unless I prepare my own nutes with salts. I am a complete amateur at hydroponics. I've been recommended to do weekly nutrient changes with my current nutes due to the 14/10/27 ratio being not ideal for flowers.
    So far my solutions have been very unstable in Ph hence me seeking a buffer method. I use RO water, which comes out at ~15ppm, Phostrogen, and Phosphoric acid for Ph down. I'm going to try to apply your buffer carefully in tests to see what results I get.

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  8. This metod has a disadvantage, the reaction of citric acid with calcium ions (from calcium nitrate) to form calcium citrate insoluble, in 2 to 3 days you will see that the solution gets cloudy. You should test with only one gallon to see what happens. Your plants will have calcium and phosphate deficiency, because citrate binds phosphate.

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  9. Hello Jaime,

    You are right about calcium citrate precipitation but I do not see a phosphate availability problem since it is not clear to me how citrate "binds" phosphate. Citrate, being an anionic entity would not interact with phosphate (which is another anion). Please post any references in literature you may have about this citrate/phosphate association issue.

    Of course I agree with your advice of doing a previous test and in all cases avoid using this buffer at concentrations above 2mM. Thanks you for your comment !

    Best Regards,

    Daniel

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  10. Hello Daniel, I don´t have any reference, only my experience. I was using a nutrient solution with citric acid and sodium citrate with the idea of mantain the pH at 5.5. After using this solution by 2 months, my tomatoes plants got a purple color (a phosphorus deficiency) and stop growing, and now they ´re useless. And they got a calcium deficiency, of course. And there´s another thing: sometimes the nutrient solution smelt funny, I think some bacteria like nutrient solutions with citrate. I´m obstinate but I gave up using citrate or citric acid.
    Then somebody told me that citrate is used to "bind" phosphate in human body for some disease, that´s the reason I wrote that, but I cannot tell.
    I think Citrate (or citric acid) is most useful in soil.
    Thanks for sharing new ideas!
    Jaime

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