No glass over the tank. none, nada, zippo, It is not a good thing in saltwater.
The white plastic is all that is needed to protect fish from jumping out of the tank. If you want a canopy over your tank, that will work fine. A great many people used them. I would have gone that route also, but living in an apartment doesn't allow me to do any building. Just no place to do it. If you choose to use a canopy over the top of your tank, make sure that the back is open and you use computer fans on the sides to circulate air though the canopy. Also try to make your canopy at least 8 inches high, this will give you the hieght to have your light off the top of the tank and let air flow under the lights to pull the heat out. And a last note: If you want to use a canopy, most light units, I am talking about the plug and go fixtures. the ones all done, are not recommended for use in a canopy. For canopy use figure on doing a retro fit. That is all the lighting componets just by them selfs. You put them in the top of the canopy and you are good to go. I know that it sound hard and scary but they aren't hard to do at all.