Something with the water. Gills look severely agitated. Need to know more about the tank. Stocking, age.. all the details. One thing I can throw out immediately. If you're only doing 20% changes with ro
than you're really not helping at all. Unless your tap is absolute liquid garbage, you'd be better off with a 60% wc
using heated/treated tap. Are you buffering the ro
water? These domestics are, more often than not, bred and raised in tap. Ro
is more for wild types and breeding.