Hi Grain!
Wanna save a few bucks?
You might not need an entirely new hood for the tank. Instead, 1 of two things needs replacing:
Either the bulb has gone bad, or the starter has.
The starter is the little can shped metal thing that rests just behind the bulb. it's job is to create a static charge towards the center of the bulb so that full ignition is achieved. When they go bad, the lights will flicker or quit altogether. The best part about the starters is that they are DIRT cheap. Just pay your local hardware store a visit and one of the store clerk will be able to direct you to the correct sized starter for your fixture.
Once you get the starter, all you have to do is turn the old one til it pops out and replace it with the new on by twisting it into place. VIOLA! working lights!
Hope this helps!