04-01-2011, 03:58 PM
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If the tubes are 48-inch, and two of them, you have plenty of light, especially without plants. I have this over my 5-foot 115g. It is heavily planted, and has done well for 15+ years.
Without plants, I would even consider a single 48-inch tube. The more light, the more algae, though again without plants that is not really an issue. And algae will handle a lot of nutrients. More important is the brightness on the fish. This does matter, depending upon the fish. A brightly-lit tank, and one with no "cover" as plants would provide, can be very stressful to many fish species.