IMO, and this is from treating massive ulcers on 20"+ koi..
I would just salt the tank to .3% right now. You would need a half a cup of salt with your water volume.
I know that african cichlids are prone to bloat/dropsy after ulcers set in, so you definitely want to catch this early. Salt for 5 days.. see what happens. IF it gets worse, do a water change and try bifuran.. also known as binox, oxytetracycline, furan-2. This is for bacteria, and I have had much success with curing the "incurable" dropsy by using this medication. This will however set your bacteria in your filters back, but I have never had any issues with it affecting the tank in a negative manner.
IF the ulcer is from bacteria, QTing the fish isn't going to do anything as the bacteria is still in the tank, so just leave him be. He won't be as stressed either.