The Hagen GLO fixture looks pretty good to me - at least it is wide enough for light from the back of the bulbs to get around the bulb to the tank. You could raise that 2 bulb fixture as much as a foot and still get good light, but with much better uniformity. It is going to be more light than is easy to manage, if you don't raise it to at least 6-8 inches above the top of the tank. Having good CO2 allows you to raise it even higher, and still get good healthy growing plants.
Now I am considering going back to unplanted with the 20 gallon tank (long story, none of it bad, but mostly to do with sig other and her plans for the tank) and upgrading by replacing it in the living room with a 40 gallon breeder. I have a thread active in the lighting forum again and i was looking for your input, on a 40 breeder which is VERY wide (16 inches?) is a single 2xT5HO fixture by Hagen GLO good enough for lighting? I will figure out a way to suspend it probably through bent conduit tubing (ceiling fixtures won't fly) - I know that 2 T5HO gives high light but I am just concerned about the spread throughout the tank. Are you familiar with this brand and their reflector? If I am better served spending my money on a different fixture (Tek 4 x 39W, 2 bulbs only?) that will provide better spread or quality of light than I can save up...
My pressurized CO2 is a shipment of fittings away from being ready, minus the reactor/diffuser!
Moss should grow very well with that lighting. CO2 isn't required, but CO2 always helps plants to grow faster and more healthy. At that light level, you probably don't need to do any fertilizing, assuming you have a normal number of fish in the tank. It wouldn't hurt to dose Flourish, which is a trace element mix, since fish poop may be deficient in trace elements.
Thanks for your assistance on that thread. With that lighting (coralife 2 x T5NO on 20g high tank - 16 inches from substrate) do you think I could do a moss "carpet" like I have seen done with plastic pieces, without CO2? I am willing to do CO2 if needed, or EI or other fert method if that would help too.
I have bought but not yet set-up (in case i decide to return), a 2 x 14W normal output T5 ( i believe) Coralife Aqualight set up for my 20-gallon-High aquarium. From the PAR chart on this forum I believe that gives me high light at the top, medium and low as you get deeper in the tank.
Does this sound like a good light to use for my aquarium if i want to grow either riccia or some other floating plant for my gourami and also cover my driftwood with moss or more riccia? Will i need cO2 to keep algae out?