High Alkalinity and low-normal pH

[ppatrick2]

I have a 65 gallon and it’s been set up for a few months now. I had two clowns, blue sided wrasse, orange spotted goby, Pygmy dwarf angel and some inverts as well as some corals. I did a water change last night and then tested everything because I had an order from WWC coming today. My Alkalinity tested at 22 dkh and my ph was about 8.0-8.2. I tested with the API master reefer test kit and the High Range pH test kit. I now have 4 dead fish and a few dead corals. I used Red Sea coral pro salt and RO/DI water from my LFS. Why is it so high? I moved all the living stuff into my smaller 10 gallon until I can figure this out. What shouldn I do?

 

[Randy Holmes-Farley Verified Community Expert]

I doubt either of those things killed fish, but if either did, it was the very high alkalinity (if real) . The pH is fine.

Do you have any of the "RO/DI" water? measure it for alkalinity.

The common way to very high a k is tap water (with its own alkalinity) plus a high alk salt mix.