Possibly Blue Green Chromis Sick

[protokix22]

I have a 60 gallon fish only with a wet/dry filter and a cannister filter. Right now, there are 2 smaller ocellaris clowns and 3 blue green chromis.

So I originally bought 4 blue green chromis, I was told they do better in bigger groups. I was also dissuaded from my original plan (two firefish and a royal gramma because they said the royal gramma was really aggressive) I'm really starting to doubt the advice I got at the LFR. The other day, out of the blue, one of those little guys died. I checked my levels and everything is perfrect. I also looked at him and there didn't seem to be anything wrong. I noticed the night before he was hovering above the substrate, not moving around, but I just thought he'd gone into "sleep mode" a little early...

Now today, I notice d one of the remaining three chromis seems to be having trouble swimming. He kind of floats around, with his body completely vertical in the tank. He can swim normal, I tapped on the glass in front of him and he swam right to his buddies where he'll swim for a while, then revert back to the vertical floating. He also seems to kind of get "stuck" on the front wall, I don't know if this is the rubbing people talk about or just poor swimming on his part. Also I read somewhere once that this might have something to do with a bladder infection. I'm at a loss because the clowns are perfectly fine, and the other two chromis are gjust fine as well.

Any suggestions? Should I move him out? Also, is this related to the other chromis death?