Another thing to worry about when covering a tank with glass is poor "gas exchange"....look for nylon "chicken wire" that they use to keep birds out of your garden. You just need to make a frame either out of wood or wire and attach the "chicken wire" to it....blocks out very little light....and keeps your critters in....so Ive been told anyway
__________________
260g mixed reef, 105g sump, water blaster 7000 return, Bubble King SM 300 skimmer, Aqua Controller Jr, 4 radions, 3 Tunze 6055s,1 tunze 6065, 2 Vortech MP40s, Vortech MP20, Tunze ATO, GHL SA2 doser, 2 TLF reactors (1 carbon, 1 rowa).
http://www.canreef.com/vbulletin/showthread.php?t=50034 . Tank Video here
http://www.vimeo.com/2304609 and here
http://www.vimeo.com/16591694