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Discus/planted tank with RO water and CO2

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  • Discus/planted tank with RO water and CO2

    I posted this under general discussions and didn't get a response. I thought I would try here..

    I have discus trace, equilibrium, acid buffer and alkaline buffer. I also have RO/DI water (the unit is shipping now) and already have everything for a fully automated pH based CO2 injection system. My issue is knowing how to use all this "stuff" with the RO water without killing my currently happy Discus... No plants or CO2 running yet.

    Current parameters are:
    -pH 6.4ish which was lowered with API's pH down from 7.6
    -That consequently lowered KH to between 0 and 40 ppm. Not good I know... I'm not sure how to get that up since the before mentioned buffers are still in the mail...
    -GH is 150 ppm

    So, I make my DI water and then add in the appropriate amounts of chemicals listed above. Then I do a big water change? Multiple small? I live in Madison Alabama and I'm told the tap water is buffered with calcium. How should I go about achieving the new carbonate based buffering?

    Next. If I want my CO2 controller pH set point to be of 6.4 or 6.5. What do I set the pH for with the buffers to have my pH controlled CO2 system inject the ideal amount of oxygen into the tank.

    I have read that the aforementioned buffers are somewhat unstable and can crash. I don't understand that. I also read that those buffers when mixed properly in RO water can read a different pH then what the mixture should have produced. But that it will read correctly once it's in the tank. I don't understand that either.

    Also do I add only pure DI water when replacing evaporated water or do I add something to it?

    Lastly, am I missing anything that I should be adding to the RO water?

    Thanks a lot!

  • #2
    Re: Discus/planted tank with RO water and CO2

    Sorry for the delay; we were unable to get to your post on Friday and we don't reply to the forums over the weekend. I just replied to your original post, but I'll repost my response here for anyone that looks at this page:
    Thanks for your questions.

    Discus Trace, Equilibrium, Acid Buffer, and Alkaline Buffer will provide everything you need to condition RO water for your discus. If you are transitioning from using tap water, I would recommend doing multiple small water changes to make the shift gradually.

    With regards to the calcium in your tap water, the RO unit will remove that in the new water and any that is already in the tank won't negatively impact the carbonate from the Acid/Alkaline Buffers.

    For targeting ideal CO2 levels at a given alkalinity, you can use a CO2/pH/KH table like the one on this forum: . According to that table, at a pH of 6.5, you would want a KH of 1.5 - 3 dKH (.54 - 1.07 meq/L or 26.8 - 53.6 ppm CaCO3) to achieve ideal CO2 levels. You may find it easier to buffer for a stable pH at a higher pH with a corresponding higher KH. The higher the KH, the less likely the pH will crash.

    When replacing evaporated water, you can just use RO water.

    I hope this helps. Let me know if you have any other questions.


    • #3
      Re: Discus/planted tank with RO water and CO2

      Right now I have two Discus, 15 neons, 1 ram, 4 Cory's, a couple Brussel noses and several plants. All plants we're put in last week.

      Plants are:
      Amazon Sword Plant - Potted
      Undulata Cryptocoryne - Potted
      Red Cryptocoryne - Potted
      Madagascar Lace - Bulb
      Dwarf Hairgrass - Potted
      Ozelot Sword - Bare Root
      Dwarf Baby Tears - Potted
      Anubias hastifolia - Bare Root

      Water parameters are as follows:
      - 55 gal tank. 48 long, 13 wide, 20 tall
      - fluval 404 canister filter with purigen and matrix
      - small inert pebble gravel with flourish tabs at the base of large plants. I didn't plan on plants when the tank was started
      - Lighting mid to hi. I have the Fluval LED 48" to 57" 5200k planted lights
      - pH of 6.55 to 6.7 fluctuating daily on fully automated CO2 injection with a carbonate base... KH is 4 degrees so CO2 concentration between 37ish to 23ish.
      - 3 degrees GH
      - phosphates .75 ppm. But I just added a little over 3/4 a cup of phosguard. That should bring it down to .02 ppm right. Is that leaving enough phosphate for the plants to thrive? FYI the phosphates derived from neutral regulator that was used a couple months ago. I know better now...

      Currently the water is being swapped from tap to RO (several RO changes have been made in the 75 percent volume range)
      The RO is reconstituted with equilibrium and discuss buffer. PH and kh adjusted with acid and alkaline buffer.

      I need a dosing regime. Weather it be with the aquavitro line or the normal seachem line. I realize this May mean I should use something other than discus trace. That's fine... I just need advice for proper dosing of this tank. I am still a noob but I am willing to do my reading and spend the money it takes to get this think on the right track.
      Any other products I should be aware of? Outside of the dosing regime I hope you will provide.

      Thank you,


      • #4
        Re: Discus/planted tank with RO water and CO2

        Hi Matt,

        Thanks for your questions. My apologies for the delay in replying.

        It sounds like you have a good set up. You've got most of your bases covered with filtration, lighting, and CO2. You will probably want to remove the PhosGuard as you start dosing.

        Conditioning your water with Equilibrium and Acid and Alkaline Buffers is great. You don't need to use Discus Buffer.

        As a guideline for a dosing regime, we have dosing charts for both the Flourish products ( and the AquaVitro products ( One of these dosing schedules will be a good starting point and can be adjusted as you see how your plants respond. Your tank isn't heavily stocked, so you might find that the plants will appreciate increased nitrogen and phosphorus as they begin to grow. You want to target levels of 0.5 - 2.0 ppm for phosphates and 10 - 20 ppm for nitrates.

        I hope this helps.