I've had my fish for about 7 years now and they all of a sudden are dying. I had a problem last summer and now over the past 2 months i've lost 3 . I have taken it to someone to check if the fish had parasites but they said no and I also took a sample is water in to them and everything was fine. But this morning I lost another one. Does anyone gave any suggestions on what I can check or do? The weather here is about 60 degrees today which is very mild here for this time of year.