It is not the pH per se that affects the fish, it is the hardness, which pH also indicates to an extent. There is also a direct relationship between pH and temperature, and imo most people keep their rays too hot.
Look at it this way: If you were trying to breed any Amazonian egg laying fish you would have a zero hatch rate in hard water as the minerals harden the egg casings before they can be fertilized. The only reason your rays appear to be OK , and even breed, is because they use internal fertilization.
Potamotrygon have evolved over millions of years to live in extremely soft acidic water, and 1 , 2 or even 10 generations of tank breeding won't hardly begin to change that.
pH is a logarithmic scale. pH 8 is 10 X more alkaline than pH 7. Rays usually inhabit water with pH 6.5 and lower or at least 15 X lower than 8. How can this possibly be good for the ray?
It is not secret that the closer you can mimic the natural habitat's water conditions the better the animal will be, and conversely, the further away you are from their ideal the worse off they are, especially from the extra stress. Hardness and pH are 2 of the biggest factors in this.
Ph 8 may be survivable but is far from ideal. The possible consequences are wasted energy expenditure leading to a compromised immune system leading to a greater
susceptiblity to parasite damage and bacterial infections, leading to slower growth and shorter lives, lower reproduction rates and generally weakened animals.
Couple this with spending $$$thousands on rays, knowing the water is not ideal yet not having relatively inexpensive accurate digital water test equipment or a decent R/O unit seems to me to be counter productive and pennywise but pound foolish. Like putting diesel fuel in a high octane engine, it just won;t work right and sooner or later will blow up in your face.
"If you ain't gonna try to do it right why do it at all?"
