Originally Posted by Githianki
Thanks for the info Byron. The tube in the fixture is only an 18" long one on my tank. Looking at your picture I should get a full length one. I haven't been able to find a dual tube fixture locally yet, but I have a few more places to check. So I would assume a dual tube T5 fixture will be a bit overkill then I take it?
T5 (which is not interchangeable with the "standard" T8 fluorescent) comes in NO (normal output) and HO (high output). The NO is basically the same as T8 would be, so a dual tube T8 would give about the same intensity as a dual tube T5. The T5 will be slightly more expensive. But T5 NO tubes are not always easy to find, depending where you live.
T5 HO is more intense than the NO or T8. One T5 HO is roughly equal to one and a half T8 or T5 NO tubes, i.e., about 1.5 times more light per tube. So two T5 HO gets you up to 3+ T8 tubes, and this is too much light by comparison. If the light intensity is beyond what balances the nutrients, plants can't use the light and algae will proliferate. Light should always be the "limiting factor" to plant growth; this way we can control things.
There is another option, that I have not tried, and that is LED. Not all LED will be sufficient for plants. And it is more expensive. I've no direct experience with LED so can't advise. I use T8 on my tanks.
I would agree that the 18-inch single T8 over your tank is not going to be sufficient. If you can find a single tube T5, I would go with that, using a HO tube with a kelvin around 6500K.