so my tank big bruise, my 6 inch and super thick Purple Spotted Gudgeon i found dead yesterday. He must have died fairly recently because his colors were still pretty vibrant but i have no idea how he died with no sign of physical damage or disease. I cant remember the day previous but at least 2 days before his death he was perfectly healthy swimming and eating and them i come home to find him belly up. The rest of the tank denisens looked fine and are fine now, however i did find it strange that when i fed them that day they fed very lethargiclly instead of aggressivly going after the pellets as they usually do. Ammonia, nitrite and nitrate all were good, but the previous water change like a 6 days prior to death i accidently overloaded the tank with the water conditioner, like 3-4 times what was needed, could that have been the culprit?