Water pH: is it better to have a pH of 6.5 or 7.5?

Discussion in 'Freshwater Beginners' started by hjreynolds, Mar 23, 2010.

  1. hjreynoldsNew MemberMember

    I'm considering 2 substrate options where the main difference is that one causes the pH of the water to stabilise around 6.5 and the other is around 7.5.
    The fish that I'm considering would do well (I think) in either pH option (angels, phantom tetras, cardinal tetras, dwarf gourami, and either a whiptail or bristlenose) and I anticipate having a planted tank

    I hear that pH can affect more than just plant and fish health, however. I didn't fully understand the explanation, but I read that it is better to have a slightly acidic pH over slightly basic as this means that following the chemical equilibrium more of the ammonia ions are present as NH4+ (harmless) than NH3 (deadly) (I might have those the wrong way around)

    Does this slight change in pH (6.5-7.5) really make that much of a difference? Are there any other issues or considerations that arise from having the water each of the 2 pH options?

  2. funkman262Well Known MemberMember

    How have you determined that one substrate will give you a pH of 6.5 while the other will give you 7.5? And how do you know that it will remain at that pH for a while and then just return to whatever the pH is out of the tap?

    EDIT: to answer some of your questions, ammonia is 10 times more toxic at a pH of 7.5 than 6.5, however, it's more important to be able to keep your pH levels steady than to try to adjust it either up or down (hence the questions above). If we just assume that the substrates truly will go to those pH levels and remain there indefinately without crashing, then what's best for the fish would depend on the characteristics of the fish. If you're wanting to keep african cichlids, I'd say go with the higher pH substrate, but if you're going with rams, the lower pH would be better. Hope this helps :)
    Last edited: Mar 23, 2010
  3. cm11599psWell Known MemberMember

    I may be wrong, but I believe having a consistent ph is more important than a low or high ph.
  4. grumpValued MemberMember

    Hi there your stocking should be ok in either PH levels... The most important thing is that the PH is stable and don't fluxuate to much... Hope I have helped Rob
  5. AlyeskaGirlFishlore VIPMember

    Most fish can adapt to a wide range. The most importent thing is consistency.

    Below I posted a link to a great article on pH. :)

  6. MindTravel3rValued MemberMember

    I think that stability of the pH is probably more important than the actual number. I agree with you that the fish you have chosen should be OK in either, but I would strive for a stable pH where the number doesn't change much over time. A rapid swing from 6.5 to 7.5 is big, and could be very stressful for the fish. Regular water changes is a great way to help maintain a stable pH.
  7. Prince PowderWell Known MemberMember

    I agree that a stable pH is most important. It is true that with a lower pH you will be dealing with ammonium rather than ammonia, but whichever it is that the fish introduce, your beneficial bacteria will feed off of it. Once your tank is properly cycled you won't have to worry about either as the bacteria will take care of it. However it does take longer for the bacteria to develop when you have a lower pH so if you wind up with a 6.5 your tank will take a little longer to cycle. In regards to which is better, since your stock will adapt either way I would choose whichever would keep your tank closer to your tap water's pH. That way you can do your water changes without having to worry about pH shock. Also, I am rather concerned about a product that is able to give you an exact number where your pH will land. If it uses a chemical additive to alter your pH then it can prove dangerous because altering your pH with chemicals will leave it unstable and susceptible to a pH crash. If it alters the pH in a more natural way I can't see how they could derive a specific number without knowing what pH your water is at naturally. You should probably look in to what the substrate actually contains that affects pH and if you discover it uses chemicals I would avoid it altogether.

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