Originally Posted by muggiwhplar
I recently bought a used MH/T5 fixture for my 75 gallon reef. It worked fine for a few days, but now the MH's will start to warm up and then shut off after a few seconds. It happens with both bulbs, and nothing really changes when I switch the ballast/bulb combinations. If it were a problem with the bulbs, I'd think they just wouldn't work; if it were a problem with the ballasts, I'd find it very odd that both ballasts were somehow damaged in the exact same way at the exact same time. Has anybody ever had a problem like this? If so, do you know what caused it?
Well first off, halide lamps are not like incandescent lamps, they aren't just "on or off." The behavior you are describing is textbook bad lamp.
However, I'm puzzled as to why both lamps would be behaving in the same way. The chances of two lamps failing at exactly the same time are about as great as the ballasts failing at the same time as you describe.
My philiosophy when buying metal halide lamp fixtures used is to always replace the lamp(s) off the bat. You have no idea how many hours are on the ones you get. What I'd recommend in this case is to purchase one or two new lamps. Put them in. if it solves the problem, great. If not, you can put the others back in, we can move onto other troubleshooting steps, and you can keep your new lamps are spares. You are going to need them sooner or later anyhow.
