This is so frustrating! For some reason I cannot keep any livebearers alive for more than a week. I have multiple largish tanks. The one I am trying to keep them in is a 55g. It is well established for going on 4 years and filtered by 2 sun sun filters (model escapes me but it is way over filtered). Occupants are 4 med sized angelfish, 5 pearl danios and 1 congo tetra (left over from another tank that crashed from a heater malfunction). Parameters are very stable 0 on ammonia and nitrites. Nitrates stay around 20 with weekly 50% water changes. Temperature is 79 degrees. I never see any signs of aggression at all. I have this 55g and a 75g discus tank and a 75g tiger barb and geophagus tank. 0 deaths in the past year except livebearers. I have tried platies mollies and guppies and can't keep any of them alive!! I don't consider my self an amateur but am certainly not a beginner but I am at a loss here. Any ideas? Thanks.