I have been a fish guy for many years, and this is the first time I have had this issue. My fish are starting to die one by one. Nitrite, Nitrate, Ammonia, PH, all is well. It is a 75 gallon tank.
I currently have:
(1)Bala Shark (down from 3)
(1)Jack Dempsey (Had 2, the smaller one died)...