[pogodzib]

There has been studies and tests from reef keepers that have light meters that show that egg crate doesn't reduce the lighting intensity at all, clean glass tops reduce the intensity by approx 8%, glass tops after a couple weeks of use without cleaning varies between 10-15%, and dirty tops can reduce the intensity my up to 25%.

1/3 gallon per day is small for evaporation. Many reef tanks evaporate multiple gallons per day.

With that lighting, I'd loose the glass top because every little bit of lost light could affect your corals greatly.

Responding back to unclejed's comments, surface agitation and canister filters won't help substantially if the gas can't escape because of a closed top. If you have a sump that gets good air circulation through it, then it may provide enough gas exchange, but that is not always the case if the sump is placed inside of a stand. The only way you can help test to see how your tank is doing for gas exchange is by testing for certain levels that can help you judge if your tank isn't getting proper gas exchange. A couple of those test are testing for dissolved oxygen and pH. Tanks with low dissolved oxygen and pH levels may have poor gas exchange, but the low levels may also be being caused by something else such as dirty water, temp, alk levels, etc...

If you setup a poll between for how many people use glass tops over a reef tank compared to how many people use either nothing or egg crate, you'll find that less than 20% of reef keepers use glass tops. And if you add experience into the equation, you'll find that beginners are much more likely to use glass tops than more experience reef keepers. Some of that might be based upon the fact that there are more beginners using less powerful lighting that doesn't put out the heat that many more experienced reef keepers use and it is tougher to keep a tank cool with glass tops.