I have a platy in a 10 gal that seems to have some white on the edges of her bottom fins. She's acting normal but I'm concerned it's an early stage of an illness as I have a 55g with a huge outbreak of idk what and it started out like this. I originally bought 4 platies and 3 of them died within the first two weeks and the last one is still going. She hasn't been in contact with the fish in the other tank but I had one of them in her tank (before she was in it) and moved it back to it's original tank after a few days. (I was trying to quarantine it but then I realized all of the fish in its original tank had it so I thought I might as well put it back). I took out most of the water and cleaned out the filter before letting it cycle and adding the platies just to make sure they didn't get sick. Maybe that wasn't enough? The two tanks eat the same food but I don't think that's the problem, it's bug bites tropical fish food. I've had her for about a month and a half and her condition hasn't changed so I'm wondering if it's maybe her colours? I don't want to add anyore platies to her tank until I'm certain there nothing wrong with her.