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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18 Responses

  1. CRUNK
    Hi, have you actually tested this in real life or only theory? Sounds very useful if it actually works
  2. Daniel
    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.
  3. CRUNK
    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?
  4. CRUNK
    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."<br /><br />What are the other problems it presents and can you suggest a more sparing set of proportions to apply this buffer? Thanks!
  5. CRUNK
    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."<br /><br />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!
  6. Daniel
    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 !
  7. CRUNK
    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. <br />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.
  8. Jaime Vladimir
    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.
  9. Daniel
    Hello Jaime,<br /><br />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.<br /><br />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 !<br /><br />Best Regards,<br /><br />Daniel
  10. Jaime Vladimir
    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.<br />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.<br />I think Citrate (or citric acid) is most useful in soil.<br />Thanks for sharing new ideas!<br />Jaime
  11. [...] solution. It's certainly cheap enough to warrant an experiment if you're worried about the cost. http://scienceinhydroponics.com/2009...c-growing.html Reply With Quote + Reply to [...]
  12. user
    Well i know this is old but hope someone might still help me here. im trying to make this buffer my self but the mix calls for 5g citric acid for 500liter so for 30liter should be 0.03g but it does not drop the ph at all really what ph should it be dropping to roughly? also should this be RO water or will tap water do? im sorry if im missing somthing but when i add the citric acid @ recommended dose to water my PH goes no lower than 6.8.. the molar mass of my citric acid is 210.14 is this the correct type of citric acid? thanks in advance
  13. Srikanth
    5g for 500 L 1g for 100 L 0.1g for 10L 0.3g for 30L. You are using 1/10th the recommended quantity.
  14. Thomas
    Hi. I have been working on an ideal method of RO water remineralization and pH buffering using goal alkalinity of > 20 ppm CaCO3 (> 24 ppm HCO3) and citric acid addition of > 0.02 g/L. My main questions follow: 1. Why is it 'bad' for CO2 to form, if using KHCO3 and citric acid? Carbonic acid is always going to form, from CO2 in the air, or CO2 from roots and microbes. Does something happen when using KHCO3 and citric acid besides CO2 formation, ex., affecting efficacy of pH buffering other than by carbonic acid or affecting root growth, etc? 2. You write about bicarbonates in your post, but you use potassium carbonate, not KCHO3. Do the carbonates from potassium carbonate convert into bicarbonates somehow, or are you referring to bicarbonates with respect to true measure of alkalinity (re mEq/L, ppm HCO3)? 3. Do you bother to calculate the added K ppm from use of potassium carbonate, and adjust Hydrobuddy according (see my use case below)? 4. Due to your informative blog post (thanks!), I won't use what I planned to use to increase alkalinity: potassium bicarbonate. That is, if there are negative effects from using KHCO3 and citric acid other than creation of CO2. That is, dependent upon how much CO2 is created and the resulting drop in pH from carbonic acid. Otherwise, I would prefer to use KHCO3 because it affects alkalinity more efficiently, I believe. That and I already did the math for needed KHCO3 per liter of RO water, i.e., 0.143 g/L KHCO3 for ~87 ppm HCO3 and 55.6 ppm K. I am using "Bru'n Water" (a free spreadsheet) to calculate the amount of citric acid to add to reach a goal pH. Bru'n Water reports final alkalinity as ppm CaCO3, after inputting starting pH, starting alkalinity, water volume and goal pH (as well as selecting acid source). From there I am using UNH AlkCalc to calculate the amount of sulfuric acid (35%) to add to reach a final goal pH (and alkalinity), after inputting starting pH, starting alkalinity and final goal pH. UNH's AlkCalc also reports the ppm of S added from the sulfuric acid. I calculated the needed amount of KHCO3 (0.143 g/L) to add to RO water for ~87 ppm HCO3. I also calculated ppm of K from the addition of KHCO3 for ~87 ppm HCO3: ~55.6. From there I use Bru'n Water and then AlkCalc. I then input the final water pH from AlkCalc, final alkalinity from AlkCalc(using "KH" in HydroBuddy is incorrect, btw), ppm K and ppm S (from AlkCalc) into HydroBuddy source water section. Optimally a grower would have her/his RO water tested a lab for alkalinity. Then add the resultant datum to 87 ppm HCO3 (converting between mEq/L, ppm CaCO3 and ppm HCO3 if necessary) for the true source water starting alkalinity. Then the grower would enter that sum in Bru'n Water.
  15. Thomas
    Darn, I forgot to write when Bru'n Water is used ( http:// sites.google.com/site/brunwater/ ) for our purposes (re citric acid) we need the use the sheet labeled: "2. Sparge Acidification".
  16. Thomas
    Neat! I just found a good conversion factor chart for using water pH, temp and alkalinity (as ppm CaCO3) to find the ppm of CO2 present in the water. I will try to post the screenshot to this message, if that fails please see the reference for the full text and the conversion factor chart: "Interactions of pH, Carbon Dioxide, Alkalinity and Hardness in Fish Ponds" William A. Wurts and Robert M. Durborow Southern Regional Aquaculture Center, Publication No. 464 (1992) http:// www. ca.uky.edu/wkrec/interactionsphetc.pdf
  17. Thomas
    Hi. So, after a bit of quick math I think I found a good application rate of potassium carbonate (K2CO3) to replace my planed use of potassium bicarbonate (KHCO3). Thanks to your warning about KHCO3 and citric acid with respect to CO2 :-D. I was going to add 0.142 g/L KHCO3 for 71.35 ppm CaCO3 (= 87.04 ppm HCO3 = 1.43 mEq/L), and 55.6 ppm K. However, after your warning I will now use 0.096 g/L K2CO3 for 71.43 ppm CaCO3 (= 87.14 ppm HCO3 = 1.43 mEq/L), and 54.32 ppm K. I just wanted to update my last message (re "Bru'n Water" and "AlkCalc") with that info, now I will leave your blog alone ... at lest until I read the next interesting blog post of yours ;-).
  18. Thomas
    Daniel, I lied, sorry! I do have one last thing to ask you: If I was trying find the increase in pH using K2CO3 (or KHCO3), from a starting alkalinity to a goal alkalinity, would the following equation work? I believe it does, according to the following web page, but I trust you more than that web page :-). http:// dataguru. org/misc/aquarium/calKH.asp log(starting ppm CaCO3/ending ppm CaCO3) So, if starting alkalinity of RO water is 5 ppm CaCO3, and the ending alkalinity (after adding 0.096 g/L K2CO3) of RO water is 76 ppm CaCO3 (5 ppm + 71 ppm), that would be: log(76/5), which equals 1.18 increase in pH. Thus, by adding 0.096 g/L K2CO3 to RO water I will increase alkalinity by ~71 ppm CaCO3, increase pH by 1.18 (assuming starting RO water alkalinity of 5 ppm CaCO3) and increase potassium by 54.32 ppm K. Correct? -- Here is a quote from that web page: (note: the abbreviation "KH" is not correct in regard to reporting alkalinity, it should be ppm CaCO3 or mEq/L.) "How much the change in KH will raise pH is calculated by taking the log of the expected change in KH log(ending KH/starting KH). e.g. if your starting KH is 40 and you take it up to 80 you should see log(80/40) = .3 increase in pH."
  19. [...] vode. Autor je Daniel Fernandez, koji je ujedno i napravio hidroponski kalkulator koji koristim. My pH Balancing System for Hydroponic Growing | Science in Hydroponics Ovo je članak o djelovanju karbonata na pH: [...]
  20. [...] Hey Spliff check out this info I found, could help. http://scienceinhydroponics.com/2009...c-growing.html Reply With [...]
    • First time reply here. Excellent blog with tons of hydroponic information not commonly found in the academic books. I've learned a lot. My question is regarding carbonic acid (H2CO3) in the fourth paragraph. There's very little literature on Google about this topic. I have a sealed grow room in a CO2-enriched environment. CO2 readings are usually in the range between 1000 ppm ~ 1250 ppm. My nutrient reservoirs are also in this CO2-enriched environment and modestly sealed (Styrofoam boards on top). What is interesting is that, while I do have CO2 canisters, I don't use these regularly, as while I'm harvesting crops and monitoring pH, EC, DO, water temperature, RH, and air temperature in the grow room, CO2 will increase (through my exhaling). I also have air pumps located in the grow room, which I'm sure are pumping that CO2-enriched air into the my water tanks. When 1250 ppm is reached, I leave the grow room. What I've found is that when CO2 readings are above 1000 ppm, the pH in my nutrient reservoirs slowly decreases (0.1/2 days). After a couple of days, I'll go back in the grow room and the CO2 meter reads 900 ppm. At that number, the pH will slowly increase. I guess the point I'm trying to convey is that I don't use HNO3 or KOH to adjust the nutrient solutions anymore (3 month trial now). I just go in and out of the grow room always checking the CO2 meter. I find this interesting. I can literally control pH by just leaving and entering my grow room at certain times. Does anybody have any thoughts about this? The crops I'm testing are doing very well. Excellent yields with bone-white roots. I'm just curious about the science of this. Is it good or not so good? Any feedback would be greatly appreciated. Josh

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