well,
IMHO, the tank that you are trying to keep all of these fish in is way to small. 2 hippo tangs, and the puffer were all going to be WAY to big for a 55. keeping them all in a smaller tank, like a 55, is a BIG no no. the tangs cover many many miles of reefs in the wild when the are searching for food. they need at least a 6' long tank, again in my opinion. the stress from the smaller tank was probably keeping the tangs and puffer stressed, and the stress weakens their immune system, leaving the vulnerable to disease.
how long has this tank been up and running and what are the water parameters ??
