So, I have no idea what happened. Our yellow tang was happily swimming and eating Saturday, then by Monday night, she was dead... All other fish, livestock and corals are doing great. We did a 20 gallon water change (25%) to be safe, but I'm still baffled by this occurrence. Any ideas what may have happened. BTW we do not have ich, all fish and livestock go through a rigorous Quarantine phase before entering the DT.