Hi Wads! You mentioned that your kitty drinks from the fish tank. ?My friend Louise & her hubby have 2 tanks. ?They finally had to buy lids for their fish tanks, as their cats were doing the same thing, drinking from them. ?I left a msg on their answering machine to ask if their cats ever developed any symptoms from drinking the fish tank water, & if there are any contaminants within the tank water. ?When I get a response, I will let you know. Just perhaps, there might be something, other than the fish, which may be giving your cat the spots in his mouth & causing his hair loss condition. ?Have you thought of posting this question on The Fish Forum; they might be able to think of something within the fish tank, which you cannot. ?Ask the fish forum people if any of them have cats & if their cats ever drank from the fish tank, did their cats develop any symptoms, etc. I would also call a couple different vets to see what they would say. ?If they ask you to bring the cat in, I would definitely take the cat in. I would also call the pet store where you purchased the fish & tank from. Perhaps they can think of something, you just never know. And it doesn’t hurt to call these various places, you would be helping your cat at the same time, as learning all this information yourself. But, these are only my thoughts. You & your kitty are in my prayers!