Hi there, I noticed a few of my platies have what looks like a bloody dorsal fin. I haven't had the chance to take a picture, but here is something that looks exactly the same (from Google). Also, mine do have red-gills as well. I was reading that the primarily cause for that is due to ammonia poisoning, however my amomnia levels are in perfect conditions. I haven't had any slight of ammonia spikes either, so I'm wondering if platties are just sensitive or maybe it caught the poisoning at the pet store?