Darkreignn,
Covering the tank with glass inhibits evaporation which is a necessary component of passive tank cooling; inhibits oxygen exchange which is vital to healthy tank conditions; cuts down the lighting even if kept clean, worse if glass gets "salty"; makes it more difficult to feed and do tank maintenance. IMHO, glass tops are never a good idea for a reef tank.
The only situations where some type of cover is needed is if you have fish "jumpers" or others that are prone to escape or if you need the extra security from small children/pets. A piece of commercial fluorescent lighting "eggcrate", available at Lowe's or Home Depot, is much cheaper than glass with none of the disadvantages.
HTH,
Dick
Just wondering if i can put a piece of glass to cover the whole tank. I am getting a 125 gallon next week. Why you ask...well I am going to put the lighting system and rather do it like that.. anyways thanx in advance to everyone that helps me out thanx...
you could but you will need a massive chiller cause you will have no evaporation especially is the peice fits tight all over. think of it as a giant green house, and those lights beating down on the water just heating it up so much. i don't use any glass and i don't have a canopy or anything i am not recomending you do this, but it allows for a cooler tank and allows for the flow in my house to oygenate my tank easier. i would suggest against it unless you are running a sump and not going to make the glass a tight fit because of the trapped heat. but i have not heard if a tight fit is truly bad, it will just be hot from my guess. plus feedin would be a biotch with the fact that you would ahve to take the whole top off. but good luck with whatever you try. just watch that temp.