Everyone's dead after adding coral beauty

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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??


Well-Known Member
Hard to say what did it. A 6 month old tank is very new. What size is the tank? This is also why a qt is so important


Staff member
Best guess is the coral beauty brought something into the tank. This is why we always recommend a min 30 day quarantine. Slightly high nitrates won’t kill fish. Mine are always between 50 and 100. I have a tank full of fat healthy fish.


Staff member
You don't mention what the nitrate level was, but this being off is not likely to kill off fish overnight. However, a spike in ammonia can kill off fish pretty fast.

Your tank is pretty small for a SW tank that could really only handle a very few small fish. You don't mention what you have in your tank, other than the coral beauty.

Also, I'd highly recommend that you incoroporate testing your own water and do it frequently (particualarly in a small aquaria). Doing so before acquariing additional live animals would be the best practice so that you pick up on any imbalance going on in your system beforehand.