Anyone change out a ballast on a sunpower ATI 4ft unit. JRL

Ok I bought a Coralvue 250 watt MH light set up for the tank one ballast runs two lamps. I have started the system and let it run both lights fire and begin to get brighter. then one of the lights goes out :doh: I swiched the bulbs to see if it was the bulb but it was the same fixture with a...