1st you need to make sure your ammonia & nitrite are '0' and your nitrates are under 20 ppm. Use a liquid test tube kit, not paper strips. Also-what size is he? What size tank? Tankmates? Water change schedule? There's no sense us giving advice until we know more. It could be something as simple as bad water in too small of a tank or it could be a swim bladder problem that's not anyone's fault. But til we know more there's no way to tell.