[hoppycalif]

You apparently have about an 8 gallon tank (48 watts giving 6 watts per gallon), so the "watts per gallon" rule isn't of much value for that size tank. Looking at the photo of the light fixture, it looks like there isn't room in there for much of a reflector. If that is true, the bulbs aren't supplying as much light to the tank as an AH Supply light kit, with it's great reflector would. The fixture is also mounted on legs, higher above the water than a standard, rest on the tank, light would be, which also reduces the amount of light the plants get. I suspect that with that fixture you have moderately low light intensity now.