Is it just new fish that die or all fish in the tank? Also what other livestock is in there? As this is in the reef forum, I was curious if you had corals ect that were doing better than your fish stock.
Edit #1
Hey, I just read apost of yours in this thread
http://www.canreef.com/vbulletin/sho...575#post240575 where you did a expanding styrofoam backdrop using krylon paint. As far as I know none of this stuff isn't made for marine use and who knows if it's safe for your livestock. You could be poisoning your fish.
Edit #2
I very highly suspect this is killing your fish. Just looked up the ingredients of kylon fusion paint. Here see for yourself.
http://www.paintdocs.com/webmsds/web...C=724504025184