I guess before anyone takes the blame here, I would have a few other questions:

Size tank, # and type of fish, Filtration, c02 duration and amount, etc

My ph starts at 7.5-7.6 before c02 injection starts. Ph comes down to 6.6-6.8 on a daily basis, which is much more than +-.01 and the fish suffer no ill effects.

My c02 is between 25-30 ppm and DC color is 6.6-6.8 according to ph color chart....... at 4.0 kh

I have good water current, but NO surface ripple, and the fish never seem stressed. I do have a high fish load as well............

I find it a little hard to believe that the ph swing alone caused this. I totally agree there is more to this story......

A very interesting puzzle though.......