Tank Coverings?

[Chin_Lee]

If you have a skimmer, it should be more than enough for oxygen exchange. One pass of water through the skimmer has more gas exchange than you will ever get through the open top of your tank.
However it doesn't address the evaporation/cooling advantage so it depends on your tank. If you have T5 or VHO or even 150de hqi over your tank, i wouldn't be too concern about keeping the tank cool. But I found a big difference when I went up to 250W dehqi bulbs that it heated up my tank considerably.

[AquaticFinatic]

Empty your mail box there sleschwin ;

[mrhasan]

I used a glass top on my 20long with 3/4 closed and the rest of 1/4 open (at the back for the filters) and I have to do top-offs with few cups of fresh water every 2nd night.