I’ve had a betta fish in a 10 gallon tank since October. The tank is cycled, ammonia and other toxic things are at 0. The tank also has 5 cardinal tetras, which never bothered the betta. My betta is REALLY lethargic, and his fins are in pretty bad shape, and i just saw a piece of fin flowing through the tank. I’ve been panicking the whole day and im really lost. Do i add salt? How much? Do i raise the temp? It’s currently at 25 degrees. He was fine and then in a matter of 2 days he wasn’t.