Sorry to inform you but if they have started fighting they will continue. Turning the lights off is like a band aid but you aren't going to keep them off. Once the lights come back on they inevitably will fight. I can't emphasize strongly enough that we must do our home work when selecting species of fish or corals for the tank.
Do not listen to LFS guys as most of them will tell you fish "should be alright" together. Here is the compatibility chart;
Marine Compatability Chart