I am starting a 24"x24"x21" Cube, w/co2 injection, AS, and am needing a recomendation on which T5 fixture to buy, and how many bulbs I need to run. Will 2 suffice or are 4 needed? Your feedback is appreciated.
24 inch T5 bulbs are 24 watt bulbs. The tank is about 50 gallons. If you have two of those bulbs you might have enough light, and with 4 you will have so much it may be hard to keep up with the maintenance. If you hang a 4 bulb fixture so you can raise it and reduce the intensity you will have the best of both worlds. This is just my opinion, of course. Some would tell you to get the 4 bulb fixture and run 2 bulbs for 8 hours, and the other two for about 2-4 hours midday, as a noon burst in lighting.
An advantage to a 4 bulb fixture is getting a better spread of light over the tank, with light able to reach more leafs from different directions.