I have a 48" double tube NO fluorescent fixture atop my tank. The bulbs are 18,000 K
Aqua-glo aquarium lamps (T-10). I have bought them only a couple of weeks ago, because the other bulbs were doing this same thing. Both sets of bulbs are flickering, and not putting out the full output. Every once in a while they kick on full force, but normally they flicker. This flicker is very rapid and to most people that look at my tank don't even notice it. Heck, I thought it was normal until I saw them click on to full power.
I do not belive it is the bulbs anymore, but would like to see if anyone knows if it is the starter, the ballast, or should I just replace the entire fixture? (The fixture is at least four years old, but not sure)