Four of my fish have died in less then a week and all at different times. What could it be. I witnessed two of the fours deaths and one of their fins or legs (for african dwarf frogs) would just give out and then they would die within 1 day. What is happening. I was thinking of doing a full water change but i'm scared that would stress out the other fish. What should I do? I have to wait for tomorrow till the stores open and then I can bring in a sample of my tank water but until then what can I do?