I was wondering if anyone would know why my small pictus cat has a swelled abdomen? It happened overnight, after a careful cleaning of the tank. It may be due to the water change, yet I have done many water changes before and this has never happened. The little guy was brought home about a year ago, and has been fine until now. It is eating, but swims with a slight side-to-side motion, instead of the usual straight zip through the water. If a picture is needed, I can try to get one.

Thanks in advance.