No announcement yet.

Problems using Acid Buffer and Alkaline Buffer with RO water

  • Filter
  • Time
  • Show
Clear All
new posts

  • Problems using Acid Buffer and Alkaline Buffer with RO water

    Hello, I was looking for some help with setting the pH when remineralising water

    I am trying to remineralise RO water to get a stable pH of 7.0. I have been using Equilibrium, Acid Buffer and Alkaline Buffer but I can't get the pH to remain at 7.

    My tank (230L) currently has a pH of 7.8 and is a tap/ RO mix. However, I am trying to switch to fully RO water through a series of water changes with the aim of reducing the pH. I am preparing the new water in a separate smaller tank first containing just an air stone. I am preparing 40L of RO water at a time and adding 13.33g of Equilibrium, 9.6g of Alkaline buffer and 4.8g of Acid buffer. The pH initially reads approximately 7.0 but then increases to 7.8 over a day or two. This all happens before I even add it to the main tank.

    The tap water is very hard and alkaline so I am wondering if a small amount of contaminant making it through the RO process is causing problems? The TDS of the tap water is 280 and the TDS of the RO water reads 29. I have tried doubling the acid dose. I have also tried using some older RO water I was saving for an emergency from when the membrane was newer (TDS 14). However, both experiments had exactly the same problem and returned to a pH of 7.8 within a day or two.

    Am I doing something wrong?

    Does it matter what order I put them in? (I have always put them in Equilibrium then Alkaline then Acid stirring and leaving a gap between each. If I put the Acid buffer in first will it clear any residual buffer that survived the RO process if that's the problem?)

    These are the readings for the water:

    Day old tap water: pH = 8.2 kh = 11 gh = 21
    Remineralised RO water pH = 7.8 kh = 7-8 gh = 8-9

    I was using standard API test kits so the pH could be a tenth or two off and it wouldn't detect it. Thank you for any help you can give

  • #2
    Thanks for the post, GeeMar!

    Once you mix the Equilibrium and the buffers into the RO water, do you let it sit overnight before using it? If so, that is likely the issue. The buffers are designed to work in conjunction with the organic acids produced in a tank, so when left in a bucket of RO water for any extended amount of time, you will see fluctuations. It is best to set the levels in the bucket of RO water and immediately get them into the tank. From there, you may need to add a bit more of the buffers if the pH shifts, but since you are using RO water, they should remain relatively stable in the tank. Of course, if you have anything in the tank that could push the pH up like specific types of rock, gravel or decorations, this could be another reason you are seeing the pH rise once in the tank.


    • #3
      Thank you for the advice but I am afraid I am still having some problems.

      I have been doing 30L water changes (using RO water and the ratio of buffers listed above) every 2-3 days and this time have been preparing the water immediately before removing the 30L of old water from the tank. The cleaning/water change takes a little while but it shouldn't be standing for any longer than an hour at most. I have done 6 of these water changes (where I have left the water standing for less than an hour). At most there should be 43% of the original water left in there (13% water change done 6 times - percentage of original water = 87% x 87% x 87% x 87% x 87% x 87% = 43%).

      However, the API pH test kit is still reading 7.8. API have quite big gaps around that pH so the next level down for the test kit to read is 7.4. I'd guess it switches to read that somewhere in the middle at around 7.6? Given that I've changed well over half the water, shouldn't I have seen a change by now?

      I don't think there is anything in the tank that should change the pH. I have some plants, decorations (all designed for fish), White Quartz Sand and a small number of polished stones. The sand substrate and stones were bought from a fish store and are listed as inert.

      Thank you for your time and sorry if I am missing something obvious.


      • #4
        I'm sorry you are still having trouble getting your pH right. So when you mention that you let the water stand no more then an hour, what is the pH just before putting it into your aquarium? What is the pH just after adding the buffers to the replacement water before the water change? Have you tried adding the buffers again once the replacement water goes into the tank and you notice the pH is elevated? You would be surprised at how little time it takes for the pH to shift in standing water, as CO2 can quickly equilibrate into the bucket causing a shift within a short period of time.


        • #5
          Hi. Thanks for the reply
          what is the pH just before putting it into your aquarium? What is the pH just after adding the buffers to the replacement water before the water change?

          The pH of the added water is 6.8 to 7.0 (depending on the batch). Exactly when I measure the pH of the water going in can vary a bit but I've never seen a noticeable shift over an hour or so. I will test that to be sure.
          Have you tried adding the buffers again once the replacement water goes into the tank and you notice the pH is elevated?

          Do you mean directly into the tank? I'm not quite sure what you mean about reacting to an elevated pH. The pH of the tank is 7.8 and seems to stay at that no matter what I do (before or after a water change). However, I'm trying to make the change gradually to a lower pH (10-15% water changes) and the pH test kit I use has a big jump below 7.8 (API test kits measure 7.4, 7.8, 8.0, etc...) so seeing a drop to 7.4 from a single water change would be surprising (and probably quite bad for the fish). If I just keep adding acid until it reads 7.4 then that seems like to quick a change that may cause some fish deaths. The frustrating part is that I don't really know that it hasn't worked until I have done 5 or 6 water changes (which are starting to get quite boring!).

          You would be surprised at how little time it takes for the pH to shift in standing water, as CO2 can quickly equilibrate into the bucket causing a shift within a short period of time.

          I prepare the water in my spare/ emergency tank and have an airstone in it to put oxygen into the water (it is basically the same setup as an actual, uncycled aquarium but without the fish). It is left overnight like that until it stabalises and then I add the buffers just before the water change. Given the setup I would have though CO2 equilibrium in my preparation tank should be similar to what it will be in my actual tank.

          My assumption is that the acid is gradually being neutralised by the alkalinity (whether from the the alkaline buffers or possibly the small amount that made it through the RO filter - our water is very hard and the RO filter is fairly cheap so the kH is still around 2 even after filtering). I don't understand how to stop that though. I tried an experiment of pouring the acid in several days early, that zeroed the remaining kH from the RO water and set the pH to 6 (or maybe below) which it actually stayed at for several days but when I added the alkaline buffer in it started to creep back up to 7.8 again.


          • #6
            When you took the KH to zero with Acid Buffer and pH to 6, did you only add back the Alkaline Buffer or did you add back the prescribed ratios? Once you have gotten the KH to zero and lowered the pH in the replacement water (30L), try to add the following ratios:

            Alkaline Buffer: 0.4 tsp (2.8 grams)
            Acid Buffer: 0.2 tsp (1.4 grams)

            I like to add the prescribed amount of each powder into a single container and then add them to the water at the same time. Let mix briefly and test parameters. If it looks good, get it into the tank as quickly as possible. Now if the aquarium has an existing KH, you may have to adjust levels directly in the aquarium by adding small amounts of the buffers.

            If this doesn't seem to work, I would recommend adjusting the levels in the aquarium. Going from a pH of 7.8 to 7.4 is not going to be bad for the fish and I think you may need to do this in order to get things stabilized. I would recommend adding small amounts of Acid Buffer to the aquarium until the pH reaches a lower level around 7.4. Once you have reached that lower level, then you need to add the buffers together to lock it in place (like I described above in a small container). Start with the following amounts after the pH in the aquarium is 7.4:

            Alkaline Buffer: 3 tsp (21 grams)
            Acid Buffer: 1.5 tsp (10.5 grams)

            Keep in mind these ratios are designed to be used in pure RO water, so if there is any existing buffer capacity in the aquarium, it is going to take a bit of trial and error to reach your desired levels.


            • #7
              Hi. I have followed your advise and tried again but I am still having the same problems.
              • I prepared 30L of RO water and added 4.8g of acid buffer in advance to zero the kH.
              • I took 30L out of my 230L tank before doing the final water preparations (to minimise time before putting it in)
              • Before I started preparing it the new water pH was 6.0 and the kH was 0
              • I then added 10g of Equilibrium, 7.2g of alkaline buffer, 3.6g of acid buffer to the new water (all added at once as suggested) and stirred
              • The new water then had pH 6.4 and kH of 4 (bit lower than planned but probably due to the acid left from zeroing the kH)
              • I added it to the tank immediately
              • About 30-60 minutes after finishing and turning the pump back on in the tank the water read pH 7.4! (No need to add any further acid as it was already reading what I was aiming for in this attempt)
              • However, I left it overnight and by the next morning it was reading pH 7.8 again

              To confirm the result I also did an experiment with the water I took out of the tank (so it should have the aquarium acids in it that the buffers need). I hoped that by doing this I could try being a bit more aggressive with bringing the pH down since there were no fish to worry about
              • I put 20L of the old aquarium water into my now empty preparation tank. pH 7.8
              • Added 0.5g acid. pH now 7.4 to 7.6
              • Added a further 0.5g acid. pH now 6.8 to 7.0
              • Added 1.5g Alkaline buffer and 0.75g of acid buffer together to lock it in place. pH still 6.8 to 7.0
              • Left it overnight with an air stone/ bubbler in the tank but the next day the pH was 7.8 again!
              This tank had nothing it other than the water from the aquarium, an air stone and the buffers I added.

              I'm at a bit of a loss of what else to do. Will switching to an RO/DI filter help? (that's going to be expensive to buy and maintain so I don't want to just try it without hope of improvement)

              Thank you for your time in replying


              • #8
                I have talked with our lab and we would suggest the following:
                Use Equilibrium first, let it mix overnight, test KH, and pH, then adjust KH to the point where the pH in the vat is stable around 7 overnight. This may take some time, but once you get the recipe you should be good to go.
                Acid and Alkaline Buffer are best used in low KH water; ideally straight RO/DI since the ratios on the label were figured out with lab RO/DI. The ratios on the label will not work with additional KH in the water. If you overshoot KH or pH in the mixing vat, add 1/8 tsp Acid Buffer then test 60 minutes later. Continue adding it until the necessary KH is reached to attain an overnight-stable pH.
                Another note is that if your tank does not generate much acid i.e. is very clean, you'll need a lower KH than the label or what might be suggested online. This will take a little bit of tweaking but you should be able to get it.