Originally Posted by jeffnsa
Go ahead and get a 2 bulb t-5 fixture. T-5's now have a very great range in the lighting spectrum for color and brightness. Hellolights.com is where i used to get my lights for when i had saltwater.
The problem with T5 is the brightness. T5 was initially developed for marine aquaria, to provide more brightness with fewer tubes than is possible with the standard T8 lights. But when used over freshwater, the increased brightness is not always good.
The commonly-available tubes for T5 are HO (high output) and each tube is approximately 1.5 times more intense (bright) light than the same size T8 in the same spectrum. Using NO (normal output) tubes will work, as these are basically identical to the same size/type of T8; but NO tubes are not easy to find. Probably because no one is going to spend considerably more money for a T5 fixture and tubes when the less expensive T8 provides the same.
I experimented with T5 about two years ago. One of my older T8 dual fixtures gave out, so I bought a dual T5 fixture (48-inch tubes). It was far too bright over the 90g it was intended for, so I tried it over the longer (5-foot) 115g. Too bright over that too [I think my fish were ready to ask me for sunglasses
], so after a week it went back to the store and I got a dual T8 fixture.
The intensity of light over freshwater is a significant issue for the fish. Most of our fish occur in very dimly-lit waters. Another issue is algae; in planted tanks, T5 HO can be too bright for the majority of plants if one is using a natural method, and algae can proliferate. With CO2 diffusion and daily nutrient supplementation, the T5 HO tubes can work. But otherwise, I consider them much too bright. A single T5 fixture would be ideal, but these are very hard to come by; again, this lighting was developed for marine tanks and there is no call for a single tube.