Planted Tank VIP
Join Date: Jul 2002
Location: Winston-Salem, NC
Unless you've got some oddball 55 gallon tank, the 48" tubes should fit over your tank quite nicely. If your tank is 36" wide, though, then I'd suggest going with either four 30 watt 36" bulbs overdriven 2x or 2-3 of them overdriven 4x.
With the four F30T12 bulbs each overdriven 2x, you'll end up with something like 3.2wpg, which will allow you to grow a considerable number of plants.
With two F30T12 bulbs overdriven 4x, you'll end up with ~2.2wpg which still isn't bad, but the bulbs will get quite hot.