[leebca]

Very sorry to hear the news.

The rather 'sudden' passing of a marine fish whether it is in quarantine or finally in the display has most often been associated with the fish not fully acclimating to its new captive life.

It is most likely this. The behavior of the fish previous to this event has me thinking that it was not doing too well at adjusting to the captive life. Hanging at the top or exposed in the corner is not the usual behavior of a new fish. However, the fish was eating and I was hoping with your care and attention, the fish would come around.

The other possibility is a chronic poisoning, with nitrites being at the top of the list. I'm unsure why your nitrite test results is showing anything at all at this stage of the setup. Are you sure the test you are using has not gone out of date? Are you sure you are using it properly? It is a test kit and not a dip stick, right?

Let the QT sit a couple of days, then it is ready for your next fish. Do not wipe anything that is inside the tank. Change half of the filter material if you wish. All surfaces contain your biological filtration bacteria and you don't wish to lose them.