Tank cover or not

[Chin_Lee]

I've read a trend on this forum before regarding the use of glass tank cover in the past but my search is not coming up with right one. The majority of the reef tanks i've seen have an open top with the lights about 6-8 inches above the water. But I also remembered people who were using glass covers and reported no problems. So my questions are:

1) what are your thoughts about a glass cover with the lights about 3-5 inches above the glass with good air vents and circulation in the hood to dissipate the heat?

2) For air exchange, would a beckett skimmer attached to a 1800gph pump provide plenty of oxigination?

3) Will it affect the coral growth? (3x250w on a 6x2x2 tank)

Any advice?
CWLee