The article cited on Koi vet is another case of sadly mistaken aquarium mythology. I have no doubt at all that the author's pond crashed, or that his fish died. But it was not the pH crash that killed them.
Fish cannot and do not read pH anywhere in their physiologic range. They are however sensitive to osmotic pressure, and our easiest (but rarely done) check on that is by TDS. IMHO, arguments pointing to denaturing proteins only apply if you have the fish on an IV or have eviserated it (which it won't survive anyway). Fish have highly tuned homeostic mechanisms and all the physiologic pathways they need to maintain their internal pH and osmotic balance against the water they are in - so long as you do change the osmotic pressure on them too rapidly. FW aquarium fish are quite widely kept in water ranging from soft and acid to hard and alkaline, or put another way, from low TDS rainwater or blackwater levels through Rift Lake levels.
Not all fish will breed successfuly over that range, because egg membranes of a number of fish are sensitive to certain minerals - blackwater fish eggs frequently cannot handle Ca++/Mg++ ions in the water - but that does not affect the adult fish negatively. Do note that neither pH not TDS was mentioned there - neither is the issue, rather GH is the issue for those fish.
Drip adjustment of water for an isolated fish is an excellent technique for altering water parameters without over-stressing the fish. I do not quite understand why some folks think of this as an extreme treatment in itself.
BTW - I'd bet on oxygen deprivation as the actual killer of the reported koi, complicated by biofilter shutdown - nitrification bacteria, unlike the fish, are sensitive to pH.
Fish cannot and do not read pH anywhere in their physiologic range. They are however sensitive to osmotic pressure, and our easiest (but rarely done) check on that is by TDS. IMHO, arguments pointing to denaturing proteins only apply if you have the fish on an IV or have eviserated it (which it won't survive anyway). Fish have highly tuned homeostic mechanisms and all the physiologic pathways they need to maintain their internal pH and osmotic balance against the water they are in - so long as you do change the osmotic pressure on them too rapidly. FW aquarium fish are quite widely kept in water ranging from soft and acid to hard and alkaline, or put another way, from low TDS rainwater or blackwater levels through Rift Lake levels.
Not all fish will breed successfuly over that range, because egg membranes of a number of fish are sensitive to certain minerals - blackwater fish eggs frequently cannot handle Ca++/Mg++ ions in the water - but that does not affect the adult fish negatively. Do note that neither pH not TDS was mentioned there - neither is the issue, rather GH is the issue for those fish.
Drip adjustment of water for an isolated fish is an excellent technique for altering water parameters without over-stressing the fish. I do not quite understand why some folks think of this as an extreme treatment in itself.
BTW - I'd bet on oxygen deprivation as the actual killer of the reported koi, complicated by biofilter shutdown - nitrification bacteria, unlike the fish, are sensitive to pH.
