05-24-2012, 10:58 PM
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Sounds like the current fixture is intended for marine tanks, if so the other bulbs are probably actinic or 420 nm or similar.
Tthe problem with what you have is not color or spectrum, but as geo suggested, the amount of light.
One T5HO tube would be good if the 40 gal is tall, as it seems to be, the problem is that no one makes a single tube T5HO at 30". Most 30" T8 fixtures have 24" bulbs, and as mentioned, this is plenty of light over a standard 29 gal for a lot of plants and would probably be OK on the 40, but you could probably use a dual 24" T8 on the 40 gal as well and stay low tech, natural - just may have to limit the photoperiod a bit.