i dont know of any filters that it would hurt, and i personally prefer submersible heaters anyway. Most heaters i have dealt with have a pretty high water line anyway, and i dont think a little bit of splashing is gonna hurt them. I agree to worry about the lights though. But i wouldnt advise a glass top for the tank. They can cause several problems. For one they will trap heat, which is often an issue because of the high lighting reefs use and the extra heat from the pumps and powerheads. Also the salt creep that ends up on the glass will block out light which isnt good for corals and clams. I have also heard (although im not sure so dont take my word for it) that just the glass it self blocks parts of the spectrum from getting to the tank.