I've had my 75 gallon tank set up now for about 3 months and had only lost on fish. Now all of the sudden I've had 4 fish die in the last couple days. I tested the water and the only real concern is the Ammonia is at .25, which should be high enough to kill the fish correct? Also, I do have a very slight case of ick from new fish, but the fish that have died did not have it. Please help!