What's The Lowest Ph My Fish Can Live In?

About pH 5. This is pretty much the same for all fish; it's where sodium uptake starts to be inhibited. Some blackwater species have adaptations which will take them down into the 3-4 range, but most fish can't cope with that. Within a range of around 5-9 any fish are fine; physiological implications only start to come in outside that sort of range.

Don't inject CO2 until you know the KH. In fact, you should never mess with water chemistry without knowing the KH.

It's an enduring myth that fish are picky about pH. Fish are only adversely affected by things which have a physiological impact. Temperature messes with their enzymes, hardness messes with their osmoregulation. But pH? Only when it's very high or very low. As long as a fish can swim, extract O2 from the water, keep its own water balance right and pick up the physiological ions it needs from the water, the pH is fairly immaterial.

"pH shock" is also a myth. The whole business of CO2 should point to this - in a tank with no injected CO2 but lots of plants and light (like mine) the pH can swing quite a bit - mine can range between 6.4 and 7.2 depending on the time of day and temperature. But the fish are completely unconcerned. What shocks fish when they're moved from one pH to another is the fact that the different pH waters are usually associated with a different TDS - Total Dissolved Solids. Sudden changes here, which affect the osmotic pressures across the fishes skin, can cause rapid dehydration or overhydration of surface tissues and from that, even death.

KarlTh said:

Sudden changes here, which affect the osmotic pressures across the fishes skin, can cause rapid dehydration or overhydration of surface tissues and from that, even death.

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KarlTh,
In the 10+ years doing Aquaria, it's the rule of thumb I've always aspired to adhere.. yet many replace 50% of their water weekly and some do 30% (or more) daily.

What's your take on this practice ?

If you are replacing water frequently in large amounts, then the TDS of the water you're using will be very close to that in the tank (unless you're doing big water modifications in the tank rather than to the water used for the changing), so it's not a problem. Problems arise when a neglected tank, in which evaporation followed by topping up has concentrated minerals, is suddenly given a big water change resulting in a sudden drop in TDS.

The other issue which can arise with a neglected tank is where pH has gradually dropped, inhibiting the bacteria in the filter. Ammonium builds up and when large amounts of more alkaline water are added the pH jumps, the ammonium turns into ammonia and the fish croak.

But as I said at the beginning of this post, big water changes where these have always been the habit are no problem.

KarlTh said:

If you are replacing water frequently in large amounts, then the TDS of the water you're using will be very close to that in the tank (unless you're doing big water modifications in the tank rather than to the water used for the changing), so it's not a problem. Problems arise when a neglected tank, in which evaporation followed by topping up has concentrated minerals, is suddenly given a big water change resulting in a sudden drop in TDS.

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That makes sense - thank you.

KarlTh said:

The other issue which can arise with a neglected tank is where pH has gradually dropped, inhibiting the bacteria in the filter.

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Interesting... CO2 can be thought of as an acidic... Per your comments, a lower PH can inhibit bacteria... Thus, there IS an adverse affect with respect to injecting CO2 though say, a canister filter inlet?

I have been pushing pressurized co2 directly into the intake of an Eheim Pro II for about 6 years and there are no issues.

I would not suggest doing this with DIY. Instead place the output of the co2 under the filter intake. Do not allow the filter to suck ditrectly on the output of the co2 as this can esult in the filter sucking the mix into the tank- and that will kill stuff fast.

finz said:

That makes sense - thank you.



Interesting... CO2 can be thought of as an acidic... Per your comments, a lower PH can inhibit bacteria... Thus, there IS an adverse affect with respect to injecting CO2 though say, a canister filter inlet?

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No more than injecting it anywhere else; the pH suppression tends to affect the whole tank. One of the pre-requisites for CO2 injection is having sufficient KH that the pH with CO2 added is not so low as to cause this problem.

I should have been more clear... With CO2 injecting diretly into the filter, the concentration of CO2 is much higher there than anywhere else in the tank.

I run two filters on my tank , each capable of supporting the tank individually. I presume the 'other' filter takes up the slack of gimped bactrtia within the CO2 'enabled' unit.

So from a 'problem' perspective (with respect to bacteria) , I imagine if it IS there, it's being masked by my over achieving other filter.

For those who run one filter and inject CO2 into it, the problem could seemingly be a much bigger issue especially if, for example, the sole filter is close to max (efficiency with respct to the various attributes).

Further, if my 'other' filter goes down, I might have a false sense of security regards the CO2 'enriched' unit supplying all needed filtration.

Finally, if the bacteria is in fact 'gimped', then I've spent a great deal of cash on CO2 distribution unit and that rubs the wrong way. My CO2 unit is now a den of stinking evil... place of decay....