There are a million ways you could probably rig something up to solve your overflow problem....from fish net to light diffusers cut to size. I would just make sure that whatever you use doesn't run the risk of getting clogged and stopping your water from making it into the overflows. As far as a new clown fish if your survivor isn't well established, putting a new clown with it might not be a problem. Adding the second one after the lights are out may be helpful. If the quarrel a bit too much you might try a little rock rearranging.