Uknown cichlid, maybe demasoni, hanging out under filter n very inactive. Was boss til a couple of days ago, now he does much of nothing except float behind filter @ top. Treated tank last week using fungus guard. Noticed large white spots on 1. Couldn't quarantine due to lack of hospital tank. So treated entire tank. That demasoni? is happy n healthy again, now the other one is sick. Both came from same pet shop n are the only 2 I've had any problems with. No visible signs of anything wrong either. All other fish in tank are fine. What can be wrong n how do I fix?