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Maintaining pH while injecting CO2

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  • Maintaining pH while injecting CO2

    I am injecting CO2 into my planted aquarium using a highly effective CO2 reactor with 100% take-up into the water column.
    In conjunction with the above, I use an adjustable pH controller that I set for a pH of 6.5. The pH of my RO water measures 6.8.
    Naturally, with such high efficiency in dissolving CO2 into the water column, the pH tends to drop quite rapidly.
    Traditionally I adjusted the pH upwards for two reasons being:
    a) 6.5 is my preferred pH and,
    b) allowing the pH to drop below the set point obviously turns off the CO2.
    While sodium bicarbonate always worked well in adjusting the pH upwards, there are a number of negative effects with the primary one being the buildup of sodium ions, which leads to the melting of some of my more sensitive plant species.
    Question: Which Seachem product should I use to adjust the pH upwards and thereby eliminating the acidifying effects of CO2?
    I looked at Seachem Alkaline Buffer, which should work, but do I need to use Seachem Acid Buffer in conjunction with the Alkaline Buffer given the acidifying effects of CO2?
    Can I safely use one of the Seachem reef products to adjust the pH upwards - which would serve my needs best without adding phosphates to the water column?

    ​Thank you.

  • #2
    Hello Fanie! Before we get into anything else, I should mention that I have never heard of sodium from sodium bicarbonate building up in the aquarium to the point that it melts plants. Sodium chloride can burn plants, but sodium as part of a bicarbonate ion is relatively benign. If your plants are melting while you use a sodium bicarbonate based buffer, it is much more likely to be due to pH or alkalinity swings, not due to a buildup of sodium. If you'd like to avoid sodium entirely though, I might actually recommend Carbonate from the aquavitro line. This will let you raise your KH and pH without introducing sodium into the system.


    • #3
      Thank you for your reply sir - may I take the liberty to post a link to a well respected source of information and post an image of the melting plants:


      • #4
        The use of sodium bicarbonate, i.e., plain baking soda, to raise pH was mentioned in one or more threads recently. In doing some research on


        • #5
          Hello Fanie! RT is correct that sodium chloride instead of sodium is typically the culprit of melting, and can appear to be more toxic than sodium because lower concentrations of sodium chloride can have a negative impact producing "drought like" effects. Sodium chloride is also typically more common in an aquarium environment than the buildup of sodium ions, because some aquarium salts can have sodium chloride as a main ingredient.

          However, sodium ions when they build up in the aquarium can definitely pose a threat to plants. Sodium can often be taken up by the plants in the place of potassium because the two elements are similar. While some sodium can be good for the plant, and help with osmoregulation, and turgor of the leaves, excess sodium can be toxic, and inhibit uptake of potassium. Some people can run into this problem while using sodium bicarbonate as a buffer, because it has to be added relatively frequently to the aquarium, so the buildup of sodium ions to toxic levels can occur. As a result of this buildup you may see melting or weakening of the leaves.

          As RT said, I would definitely recommend trying out carbonate from the AquaVitro line! It is potassium bicarbonate based, so you can add it relatively frequently to keep the KH and pH stable, and you'll get the added benefit of potassium ions instead of sodium :)

          I hope this helps!


          • #6
            Thank you for your feedback.

            As an interim solution I bought 1.2 kg Seachem Alkaline Buffer which buffer my pH at around 6.8 with the pH controller set at 6.5
            Question: What precautions should I take when using Alkaline Buffer as I found that I have to initialy use significant amounts (6 to 8 teaspoons dosed in solution over a period of 24 to 48 hours) when using the buffer to compensate for a reduction in alkalinity while injecting CO2.


            • #7
              My recommendation would be just to keep a close eye on your pH and alkalinity, ensuring there are no drastic swings while you are adding the buffer.