I need some help! I have a 55 gallon planted tank full of Rummy nose and cardinal tetras. Maybe 20 total. Yesterday I noticed that one of the Rummy nose has lost its tail and the back half of its once clear body has become cloudy. Is this tail rot? What is the best way to treat this with a planted tank? Overall the tank has been super healthy for some time and I cannot understand why this would happen. Any suggestions?