so everythign was okay, you added the clowns, one was not doing well (it actualy looked liek acclimation shock to me... how did you aclcimate them and for how long?) and then the next day everythign was DEAD?!
what else did you do to the tank in the time of the clownfish to now? water change? perhaps there was something in the bucket? soap for washing it out or even that was on a towel you used to dry it? did you stir up the sand bed at all possibly trying to catch one of your many many fish?
perhapds DO levels? what type of waterflow/filtration do you have?
good luck
if you can tell us everythign that you ahve done since adding these fish and also all the symptoms of all the fish (IE, heavy breathing, white film, white/black spots, not swimming well, redness, pale, light breathing, etc, etc, etc)
good luck
and yes... how old are you test kits?