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  1. #1
    Hi, I'm New Here!
    Join Date
    Apr 2017

    PH control with CO2

    I have a large planted tank 200G with overflow and sump. After several tweaks on the plumbing, I have virtually no surface agitation and ability to overdose on CO2 (based on my history with this tank, a good thing). I am getting Discus and want to be more careful with the CO2 swings. I run the CO2 8 hours a day inside of a 10 hour lighting period. Without the PH controller, my PH would peak at 7 (my tap water PH) just before the CO2 would come back on, and then during the 8 hour CO2 cycle dip to upper 5 or lower 6, depending on my bubble count tweaks.

    Here is my question on setting up my controller...with domestically bred Discus, should I:

    1) run my CO2 24 hours a day with the controller auto shutting it on and targeting a specific PH - I have tested it and can keep it very stable at 6.3 to 6.5, and still get ample CO2 into the tank. This way the PH of the tank will be at this value 24x7 as I will be running the CO2 at night as needed for this PH.

    2) run it on the 10 hour lighting cycle, shutting it off at night and allowing the PH to creep back up to 6.8 or 7. This way the daily PH flucuation with by 6.3 or 6.5 to 6.8 or 7, not insignificant, but not huge.

    Assuming both approaches are equally appropriate for the plants - which is better for the Discus?

  2. #2
    Just an Egg
    Join Date
    Dec 2013

    I have used both methods over the years with discus planted tanks. One lesson I learnt the very hard way is to make sure that if for some reason the solenoid fails or the power cuts off the valve allowing CO2 into the tank shuts off. Mine many many years ago was the other way around and I came down to a tankful of suffocated discus I’d been growing for 5 years.

    Also remember plants will expel CO2 at night so depending on how many this can alter your ph.

    Today I am running CO2 with plants and only run the CO2 during the day when the lights are on. According to the Seneye device and my own testing my ph only increases about .2 after the CO2 turns off and this seems to have no ill affects on the fish.

    Also only running the CO2 8 hours instead of 24 it will last quite a lot longer. I also don’t these days use the CO2 to maintain a set ph, just run a steady bubble stream. I found using a ph probe became a pain and they always seemed to get lose calibration and cause more problems than they were worth.

    So if it was me I’d use a solenoid on a timer that matches my light timer and just set a constant stream for that time that works for you.

    That is what I’m doing today, although I am still adjusting the dose as I removed a lot of plants and am trying to get them to petal again. Am awaiting the CO2 measuring device you stick on the tank to turn up as we speak to gauge how much CO2 I have in the tank. My guess is I am well under what I could have but don’t want to crank it and have an issue.

    Hope this helps, at the end of the day it all works but most important from my experience is a solenoid that shuts off if it fails not stays on.

  3. #3
    Join Date
    Nov 2011
    Terrigal, Central Coast, NSW
    I've just started a planted tank with CO2. If you're running a sump you'll need a way of sealing it off so that you don't lose all of your CO2. Simply having lids on your sumps and putting some gaffer tape over them is sufficient.

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