I'll give you some of the same info I gave another guy below.

You must take into account the efficiency of the flourescent technology.
T12, T10, T8, T5 are all increasing in efficiency. T12 is the old stuff
with lowest efficiency. The watt/gal ratings were developed a long time ago
during that period. A PowerCompact is T5 and worlds apart from an old T12
bulb watt for watt. Wattage alone does not determine how much light is
produced. You must define the effciency. You need to consider lumens per
gallon not wattage per gallon.

I have a 100G tank and use 2 - 55W 24" 6700K PowerCompacts. That's 1W/G of
T5 technology. More than enough light. I have O2 bubbles coming off my
plants. Would not want more light, unless I was trying to raise plants for
sale needing ultra fast growth.


T5 PowerCompacts are nearly as efficient as Metal Halide. MH may appear
much brighter, but that is due to the concentrated point source nature of
the light. The total light output is not much different watt for watt. MH
produces the shimmer effect because it is a point source, and therefore
casts strong shadows. Flourescent does not because the light is spread out
over a long blub thus eliminating shadows. Flourescent is diffuse lighting
which is much better for a freshwater tank.

It is important to realize that you must balance light, nutrient, and CO2
levels. Having too much light means your plants will need tons of nutrients
and CO2. Continuous feeding at very high levels forever.

It is not necessary nor desirable to light a freshwater tank like a reef
tank. There are no trees out in the ocean, but there are lots of trees over
streams. Most natural streams are largely covered in shade and most
freshwater fish care little for bright light.

Chris.