I purchased the majority of my fish here and all have been perfectly fine. After having the tank up and running successfully without any deaths for 6 months, I decided I wanted 1 center piece. So I purchased a coral beauty angel from the local pet store last weds. She immediately hid and wouldn't even come out to eat. By Friday, my first fish died. Saturday, both clowns and the angel were dead. So I called the pet store, they tested my water and said that my nitrates were a little high and this is probably what caused the death. He recommended a water change. So I changed 30% of the water, checked all my levels. Everything was good. Sunday morning every fish is dead except lawnmower blenny and water is cloudy. Tested water. Ammonia spiked overnight after water change. I put an ammonia detox in the tank and tested again at the end of the day. Ammonia was almost gone, all other levels were still good. Now today all levels are perfect, but the lawnmower blenny is dead. So all I have left which doesn't seem effected at all are my crustaceans and snails. WHAT HAPPENED??