It is just my opinion, of course, but I think that a lot of people tend to diagnose illness as the cause rather than the result of stress. I have enjoyed great success with Discus using a fairly simple but increasingly unfashionable formula - plenty of clean water and not succumbing to the temptation of 'adding one last fish' to my tank.
TGWH says he has a planted community tank, so although some of the advice given here might be fine otherwise, its difficult to apply to a planted community tank without collateral damage. Plants will struggle and even begin to decline at temperatures above 28 degrees (so that will increase his phosphates again), and other fish (depending upon what they are, of course) might also struggle at that temperature. Medicines always have a negative effect on bacterial and microbial populations but their use can be easily avoided by not stressing the fish out in the first place.
Just my 2cents.