Hi Alfred - glass tops definitely cut back on evaporation, even drastically so for certain tanks that have a significant surface area to volume ratio. I don't have any links regarding the subject, but have been using them for years without issue (albeit in a house with central sir so overheating is not an issue). Gas exchange is certainly a concern if one were to have little water movement, but that is never a concern in any reef tank, especially one with an overflow and protein skimmer.