Hi I have 6 neon tetras in a 29-gallon tank. I noticed one of them has the left fin looking like snapped to the side and white. It swims well and eats well. No sign of discomfort from that fish. Any idea how this happened? Should I be worried and take some actions?

Summer is approaching again. Last summer, I had a lot of trouble keeping the temperature in my aquarium at 30°C. My fish prefer 21-24°C, but I couldn't get it any lower than 30. So I want to avoid having to go through all that trouble again, and to keep the fish happy. I doubt fans are going to h...