I suspected something in your filtration system but wow a decomposing ray pup. This is something out of your control..... don't feel too bad. Had you not physically checked your filtration system, more than likely ALL of your stock would have been wiped out. I feel for your loss, but now concentrate on those that did survive.....
Massive water changes (50%), and double the regular dose of prime for the next couple of water changes. Best of luck.
Massive water changes (50%), and double the regular dose of prime for the next couple of water changes. Best of luck.