Unfortuanatly your in a cycle that will only be broken by full tank and stock treatment of ich. Although the other fish do not show signs, it is very present in your tank. Any futher additions, and eventually, probably your other live stock will get ich. Get out to Wally world and pick up as big a tank as you can afford, heater, filter, and pvc
fittings and get ALL your fish in qt
. Treat them with hypo or cupramine, a copper based medicine. Trust me it works! With all the money you have spent on deceased clowns, you could have a qt
. Please do yourself a favor, and do this. You will battle this from here on, until it makes you give up the hobby. Godd Luck my friend.