I've got 6 bulbs total of T5 on my tank; a 4-bulb IceCap retro kit and a 2-bulb Tek retro kit. I'd recommend going with only IceCap. They have nicer reflectors (both IC and Tek are individual reflectors, ie each bulb has a reflector that clips onto it), the IC ballasts are much nicer and will overdrive the bulbs, giving you more watts, (note: you must figure out a way to install a fan or some manner of cooling breeze down the length of your bulbs if you overdrive them, as overdriving will shorten the lifetime of the bulbs if you let them get too hot) and the wiring harness on the IC kit was much nicer, simpler, and more professional than the Tek kit. Lastly, I can't prove it, but I think the Tek ballast is so electrically "noisy" that for the first year or so it would trip my GFCI outlet daily.