hmmm, wonder why ppl over drive them to begin with, thats expensive, replacement every 2 months. Might as well put metal halides, complimented by VHO's, highlighted by T5's wrapped around in leds.
Based on how your tank looks with a cell picture I am going to guess that i am currently running 36" T5HO bulbs on a regular ballast. I upgraded my bulbs to super blue and purple plus on a very reasonably priced light fixture. I have been meaning to open it up to confirm my what I suspect...T5 ballast and I installed HO bulbs, not getting the most out of it.
Anyhow, this research is for the lighting that is going to go in the 120 gallon, its a 4ft tank. trying to decide if T5 fixture or VHO retrofit.