Keeping the pH of your hydroponic nutrient solution stable

A nightmare for many growers inside the hydroponic industry is the fact that pH adjustments need to be made every now and then to nutrient solutions. In fact, people often adjust the pH of their nutrient solutions several times a week in an effort to keep the values close to those considered ideal. However, most growers are unaware of the basic facts surrounding pH changes and how they can be avoided (please refer to the pH FAQ for more information).
The concentration of H3O(+) ions, which are the ions that determinate pH, changes according to other ions present inside the hydroponic solutions. Since plants take ions (which are charged species), outside of the solution, they cause a charge imbalance which is compensated by the generation of either H3O(+) (if the plant absorbs an ion with positive charge) or an OH(-) (if the plant absorbs an ion with negative charge).

One of the ways in which this pH change can be effectively controlled is by the addition of a specie which balances out this charge and offers reactivity against either OH(-) or H3O(+) species. Such addition of species to a solution in order to offer a chemical equilibrium protection against pH changes is called “buffering”. In hydroponics, solutions are most often “buffered” using ammonia, however, we can carry out simulations to see how this two ions act against “acid” or “base” additions and see how the entire hydroponic system reacts to this.

The simulations are carried out using the Maxima software and all the equation systems are generated according to equilibrium equations, mass balance equations and charge balance equations (this is called systematic study of the chemical equilibrium). Concentrations for all the buffering agents were treated as 0.1 mM.

Long story short, the graph below shows the results for my simulations of “acid” or “base” additions using three different buffer agents. The blue line shows the change when citric acid/citrate is used as a buffering agent, the orange line shows when ammonia is used as a buffering agent and the yellow line shows when carbonate/citric acid is used as a buffering agent.

As it can be seen, citrate provides very good buffering capacity towards acid pH values while it’s buffering potential towards basic pH values becomes lesser. Ammonia provides almost no buffering potential towards acid pH values while it provides almost the same buffering effect towards basic pH values than citric acid. Note that basic pH buffering seems the same for both buffers because here the effect of the phosphate ions inside the solution becomes more prominent.

However, when carbonate/citrtic acid is used as a buffering agent, it suddenly turns the solution’s buffering power towards both acid and basic pH values, extremely high. That said, it should be expected for a solution with this buffering mix to last several times more than a regular solution without needing any pH adjustments. In practice, the preparation of this solution has given me at least three weeks of plant intake without any need for pH adjustment.



  • joey
    April 26, 2010 @ 1:22 pm


    i have a question about the pH.
    I am culturing duckweed.
    First I was using a Hoagland E+ medium, with adjusted pH to 4.6, as written in the manual.
    When renewing the solution (after 2-5 days), the pH had increased to 6 or higher.
    Now i am culturing them on a hoagland and arnon solution, and adjust the pH to 6, as said in the manual. but now, the pH had decreased to 3.5-4 when renewing it.

    Do you know why?


  • Daniel
    April 27, 2010 @ 11:49 am

    Hello Joey, Thank you for your comment. Your problem could be caused by many different factors. Initially a solution could have a pH increase/decrease due to several factors included but not limited to the buffer capacity of the growing media, the hardness of the water, solution quantity, etc. From what you describe it seems that your problem is a lack of enough solution which causes a rapid absortion of nutrients and a loss of balance within the solution. This causes a pH increase in the cause of a nitrate rich solution and a pH decrease on more cation-rich solution. To solve this problem you'll need to verify that a) you have at least 1 gallon of solution per plant b) the media has little or no buffering capacity c) the ammonia/nitrate ratio of your solutions is accurate. I hope this helps ! Thanks again for your comment,Best Regards, Daniel

  • holzdan
    May 17, 2013 @ 9:22 am

    What do you think about adjusting the ph of tap water prior to adding fertilizer. I got tap water with ph of 8 ec of 120 ppm with a carbonat hardness of 5-6. I tried this and lowered my tap to 6.8 with citric then added nutrients and it ended at a ph of 6.4. Then i adjusted my ph to 5.8.After ca 16h it jumped back to 6.5 , so i added some phosphoric and since then it keeps stable.i also noticed some foaming (not really much) in my nutrient solution when im using citric .. why is this happening , should i be concerned about it ? what do u think about adjusting ph to a more acceptable range with tap and citric before adding fertilizer and readusting after another time ?

    • admin
      May 17, 2013 @ 1:54 pm

      Thank you for your comment :o) Please feel free to make a 20 USD donation to HydroBuddy and I’ll be glad to answer your questions. This helps me support the software,

      Best Regards,


  • Khairil
    November 5, 2014 @ 5:32 pm

    Hi! I’m growing my seedling in the 50% Hoagland Solution. I wonder why the pH is not constant as what I set up (pH 4.0).The pH rise from 4-6.5. Is there any suitable buffer for my hydroponic solution? Because I am tired to check the pH and drops some HCl into the solution several times a week.

    May 24, 2020 @ 10:14 pm

    What is the procedure to implement that ammonium and citrate buffer ? Do you have a curve of that buffer or you just added the benefits of the citrate and ammonium curve together ?

    • admin
      May 25, 2020 @ 8:24 am

      Thanks for commenting. Although citric acid/citrate seems to be a good buffering tactic in theory, in reality plants will strongly uptake citrate and aggressively move up the pH. For this reason a carbonate/ammonium buffer is superior, although in terms of pure chemistry the citrate buffer seemed better. However – since ammonium can easily become toxic – it is important to keep the concentration of ammonium below 20% of the total nitrogen used. Read this post for more information about the carbonic acid/bicarbonate buffer in hydroponics.

  • Mikeschaerer
    September 4, 2020 @ 1:31 am

    It would have been nice if the PH / concentration chart included a line which showes how high the PH is if there is not buffer within the solution (as a reference). Keep up the good work, this is the best site on hydroponics I have discovered so far…

    • admin
      September 4, 2020 @ 11:37 am

      Thanks for your comment!

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