Hey 99 sorry to hear about your loss. I'm glad to read that you want to stick with it. That says alot about your character. As ofk said adding the fish too fast was probably what brought this on so quick. There is bacteria that lives on the sand and live rock that breaks down ammonia (waste products from fish). It takes time for the bacteria to grow. When you add a fish the bacteria will increase according to how much ammonia is available. This also applies to how much food goes onto the tank. It sounds like you have enough sand and rock for the bacteria to call home. When I started I added a fish every two weeks. By the way, I have a 40 gallon and took my LFS advice and got a flame angel and blue tang. I realize now that both are too big for the tank.