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pH question

Discussion in 'Fish Keeping Chat' started by magpie, Jul 13, 2020.


  1. magpie

    magpie PetForums VIP

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    As I understand it, the nitrifying bacteria that we need in our filters becomes less efficient or starts to die off when the pH drops too low. What I want to know is, is this always the case and if so, how low is too low?

    My new set up (the 60 litre) is still cycling at the moment and the pH is getting very low indeed. Will the tank cycle with a low pH, and will it stay cycled? I want to keep softwater fish so I'm happy for the pH to be low and I didn't really want to have to buffer unless it became absolutely necessary, but is it going to cause problems?
     
  2. LinznMilly

    LinznMilly Moderator
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    Yes, if pH gets too low, the cycle will stall. Likewise, in a cycled tank, if pH gets too low, the bacteria go into a sort of hibernation.

    As for levels, at 6.8, bacteria are working at 80%, and then it drops roughly 10% per point, so 6.5 = 50%. 6.1 = 10%.

    The saving grace is below pH of 7, ammonia atoms change to become more ammonium ions (NH4, not NH3), and the lower the pH, the more ammonium is produced. It's basically the natural equivalent of Prime.
     
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  3. magpie

    magpie PetForums VIP

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    Thanks @LinznMilly, I knew you'd know!

    I am confused though because as far as I can tell my cycle does still seem to be going, as ammonia & nitrite have both dropped since yesterday and nitrate has gone up. But I bought a pH meter as the API kit doesn't go lower than 6, and my pH appears to be 5.3 since yesterday at least. Have I screwed up the cycle by letting it get that low?

    I've asked on a couple of Facebook groups too and some people are saying I should buffer because the tank won't cycle at that pH and some are saying the opposite and that their tanks are fine and cycled at this kind of pH.
     
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  4. LinznMilly

    LinznMilly Moderator
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    Optimal pH range for nitrifying bacteria is between 7.5 and 8. Some sources say that ammonia may continue to be converted to nitrite at pH as low as 5.8, but the nitrite bacteria need pH above 6.5. Bear in mind that the cycling process is affecting pH as well as the pH affecting the cycle.

    I'd carry out a water change to bring the pH back up. :)
     
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