Sorry Aquadream, pH fluctuations do depend on KH.
As an illustration, a 20 PPM increase in Co2 may lower the pH by 0.8 in low KH water, while the same in increase in Co2 may only lower the pH by 0.1 in high KH water.
The fish don't mind the pH change as such, as it is not paired with a sudden change in TDS, so it won't shock their Osmoregulatory system.
When people talk about fish being sensitive to pH changes, they usually mean that they are sensitive to TDS changes, which are often coupled with hardness and pH changes.
Hope this is clear
If KH is stable in any given aquaria then the PH fluctuations will not depend on it but on CO2 fluctuations. KH is suppose to be the buffer capacity of any aquarium and assist in keeping the PH stable, not the factor that causes PH fluctuations.
We can smart argue forever over this, but KH unstable tank is basically a recipe for disaster.
So when you make a statement against another statement remember that this is not philosophical discussion considering all possibilities, but in particular a stable aquarium.
Other wise PH fluctuation can depend on more than KH and CO2 if we get to dig too deep.
PH can change where TDS can remain constant because PH depends on CO2 and TDS does not. Also PH is related to TDS, but again TDS is suppose to be a relatively stable parameter in aquarium. TDS would not change significantly ever if we do not add fertilisers. Of course you could go onto the water evaporation, but there the answer would be simple to. Top up with RO will prevent huge changes in TDS readings. So your second statement is quite incorrect am afraid.
I would say the discussion should revolve around the basics of stable aquatic environment, not around what could happen or how many chemical possibilities are out there, because that would get on the way of the hobby.[DOUBLEPOST=1396644428][/DOUBLEPOST]
Yes, of course changes in pH can affect fish independent of TDS, but they are much more sensitive to TDS and hardness than they are to pH.
Fish have been found thriving in parts of the Amazon where the pH is about 6 at night, and about 2.5-3 during the day.
PH 6 at night and 2.5-3 during the day??? Are you sure is not the opposite. In nature CO2 will build up in aquatic environment at night not during the day. So at night PH will be lower, because during the day all plants will use up the CO2.
If TDS is stable in aquarium the fish will not be sensitive to it. So instead of getting at what the fish can be sensitive to you should be looking up for stable parameters in your tank.
