I'm looking to upgrade the lighting in my 15 gal column tank so I get better growth out of my plants. Right now the fixture only uses 1 T5 8 watt bulb, which doesnt really do much, especially for the ground cover plants. I havent been able to find a fixture though that would fit. I am hoping to have 4 bulbs, but if I can only get away with 3 that would work too. I was looking into "u" and circular bulbs, but all are too big so far. Dimensions are 13.5 inches x 13.5 inches.