Sick fish

Initially the female platies looked significantly stressed, but since the major water change it has been the males that look worse. Basically the water change sent to platies sex mad, and the largest male started bullying the smaller males. The second largest male is the one the got the most harrassment (perhaps because he was more willing to stand up to the largest male, unlike the smaller males who just ran). Anyway, he has had a moderately large whitish patch at the base of his tail fr a couple days - it looks more bacterial than fungal, but I am hesitant to add an anti-bacterial to the tank for fear of disrupting the biofiltration. I added Stress Coat - not sure if it will help, but anything that speeds wound healing (it's basically aloe vera) has some potential to help the fish. I'll see what happens - if need be, I'll isolate him and treat him with something stronger.