Today I was changing 2.71's water and I noticed I really bad smell. I cleaned out his tank and moved him from the 2.5 gal he was in temporarily back to his 5 gal. I smelled the water before I put him back in and it was fine, but shortly after it smelled just as bad! I think it must be him because I changed Sqrt's (my other betta) at the same time with the same water and his tank smells fine.
Is this some kind of illness that is making him stink, breath heavy, and barely move?
I checked the water stats and it's all normal and the temp is 79 degrees.