Well, for starters, that is a lot of fish for a 12 gal tank, especially if you have only been set up for month. You should only add a fish every 3 weeks, and i would say in a 12 gal tank, you should have a maximum of 2 fish.
Also, clowns are aggressive fish and should have been added last if you wanted to add a peaceful fish like the firefish. And that tank is too small for a 6 line anyways.
You can try doing a black out, or re-arranging the rock. But i think you need to get rid of either the clown or the firefish for peace and correct stocking.
Nijahed by biff and her speedy fingers