Could you describe it in more detail i.e how big is it, wether it is in streaks or one big blotch, does it have any texture- is it fluffy looking, inflamed or lumpy etc? Can you also post nesarsary water stats too please
white spot is a parasite and melafix will do diddly squat for bacterial infections, its only of use for helping to repair ripped fins. can you get a pic of it?
are these the new fish you got chish? if so didnt you quarantine?