10-15-2012, 05:34 PM
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Susan, there must be a glass cover between the light tubes/fixture and the water. This can be a glass cover on the tank with the fixture above it (I use this method), or it can be a fixture that includes a built-in glass cover. Without this, water is too likely to splash on the light which can explode the tubes when hot, rust the prong ends, and get into the ballast or whatever. And many fish will jump so they will be fried against the light. As i want my tanks fully covered to save fish that jump, retain moisture and keep dust out, I use the glass cover. With this you are free to get almost any fixture.
If you have a standard 4-foot 55g, it will have a lip around the inside of the frame at the top, and you can buy a glass cover set that sits down on this. Then you buy a light fixture that sits on the tank frame itself, not on the glass.
You have some options. I would stay with T8 (the regular fluorescent) and not T5, over a 55g. A dual tube T8 (holding two 48-inch T8 tubes) will provide good light. A dual T5 will be too much. A single tube 48-inch T5 would be fine, but these are no longer being made as far as I know.
There is also LED lighting, but I have no experience with this so won't say more, except that they are much more expensive and you have to know exactly what you're getting.