This same topic comes up about once every 3-6 months somewhere and has for the last 15 years I've posted on line.
When you add CO2 enrichment, it does NOTHING to the KH, it will change pH but has no effect on fish.
I have done massive water changes using the same KH, but the pH is often 1 full unit different and fish are/have been fine, as they are for everyone that does large water changes on CO2 enriched planted aquariums.
No one adjust their pH before adding replacement water, that would be a huge PITA to say the least.
Since few if anyone does this..............why do planted aquarist not have any issues with water changes and fish? I've bred dozens of fish, shrimps, all sorts of stuff.
Why is it that fish can adapt easily to differences in CO2 and pH, but not say......salts.......like baking soda? Is CO2 a salt?
pH is a poor measure for fish preference because pH moves all over temporally and spacially. Fish move around all day long, who knows if that one single measure of pH is representative of the system where someone took that measure 18 years ago?
Maybe it was after a big rain, or only during the dry season.
You do not know and neither do they. Without looking at the entire environment ranges, we do not really know, we also assume that what is in nature is best for aquaculture, this may or may not be true, we cannot assume that either.
Regards,
Tom Barr
