Will a 24 watt T-5 bulb over a 20 gallon tank put me into low light territory? My options are 1x24 (1.2 wpg) on the tank or 2x24 (2.4 wpg) hanging. My goal is a medium-ish rate of growth (stems, crypts, dwarf sag) and if the 1 bulb can get me there I'd prefer it, but hanging a 2x24 is feasible. Either way there will be an inconvenience, waiting for the glass lid to come in or having to build the arms. Opinions?