I have had my tank for four months now and all the fish have been healthy. Now, one of my platys has a problem with her tail. It does not seem rotted, but it seems to be shrinking. It is clumped together. I'm not sure if its fin rot or something else. I don't know my water parameters...I have to get a test kit tonight. I also don't have a quarantine tank. I know, I should have one, but I didn't have room, and it was something that I was planning to get and never did. Even if I set one up it wouldn't be cycled.....anyway, I am not sure what the problem is. She is moving fine and eating normally, but her fins look like someone reached in and squeezed them. I immediately did a PWC, removing 40% of the water. This did not seem to have any effect. The temperature in the tank has been difficult to maintain lately, with the wide swings in temperature in the room. It was 75 this morning, now it is back up to 80. I know that is very bad. Is that what brought this on? All my other fish seem healthy and are unaffected. Please help!