Originally Posted by Sniperhank
That might be your issue. Water changes are necessary in order to keep ammonia and nitrites down because you won't have anything to hold beneficial bacteria in there, be it live rock or filter media. I would suspect that ammonia and nitrite levels did in your clown tang as the water changes weren't daily to manage these poisonous elements.
He did say he has two sponge filters in there, but didn't mention if they were cultured or new.
If they were already cultured with BB, I doubt a tiny clown goby would produce enough waste to pollute the water that much, plus he said he tested and it was ok.
I say it was most likely not healthy to begin with without more info.
A new fish dying within a day or two of getting it isn't unheard of and often it has nothing to do with what/how you did things.
but, to be on the safe side I would clean the QT tank out, let the filters and tank dry just to be certain there aren't any pathogens present.