this is bothering me a lot now. i found my powder brown tang dead yesterday, and this morning my harlequin sweetlips. both were found almost in the same spot at the bottom of the tank, near the back left corner. neither had any signs or symptoms of disease or stress before they died, both seemed to just drop dead out of nowhere. both were eating fine and swimming about up until their death. my harlequin sweetlips was eating prawn and mysis daily for the 3 days i've had him, and my pbt was eating mysis and pellets for the last month ive had him. what could be causing this sudden death in my tank?