This is the third angel in this tank to have this. First one was a few weeks ago, everyone else seemed fine. Developed a bloated abdomen, passed after three days. Second one did the same thing last weekend, and now a third one is doing the same.
78 degrees
25 nitrate
0 nitrite
0 ammonia
200 ppm gh
80 ppm kh
6.8 ph
0 chlorine
no new fish or changes, any ideas?