I have 6 adorable Pygmy Corydoras and one suddenly has no tail. My water is fully cycled, 10 dKH, 7.5 PH, 1 ppm NO3 and 0 NO2. Water changes: twice weekly, one small, one larger. No other fish have this trouble, and I can't figure it out. This guy shares an 18 gallon tank with a few neocaridina shrimp, endlers, dwarf rasbora and ember tetra. Can this cory survive without a tail--does it grow back so he can swim more normally? Should I worry about this spreading to others as some sort of infection?