One or Two, Dual T5HO Hagen GLO 48" for 75 gallon?

http://www.plantedtank.net/forums/lighting/117002-watts-per-gallon-sucks-rating-light.html

read post #5 by Hoppy

let his tests/research/hobby help you in making a decision

I think a 75gal is about 21" tall..good luck!

So only one fixture will be needed. I misread it last time and thought one would be too low.

I can also always hang both lights in the future.

I'm going to get both and do a 2 hour burst with one of them, alternate each day which fixture is on the full time.

Will 2 hours a day of too high light cause problems? Or I could have one light near the back on for 5 hours, then the front one turns on 3 hours in, for an additional 5 hours. Total photoperiod 8hrs with 2hr burst, and simulating the movement of sun

I'm confused by your initial post- will you be running CO2 on this tank or not?

I run 2x54 T5HO over my own 90gal and it's alot of light, I can only run a 6-7 hour photoperiod without running into algae issues since I'm not running CO2 on the tank. Someday I may switch my fixture out for T5NOs, or perhaps hang the fixture higher up off the tank.

So definitely don't get 2 fixtures unless you're setting this up with pressurized CO2. If you are, then go for it- and you can experiment with your photoperiod to your heart's content to figure out what will give you best results. Every tank can be a little different in that respect.

Thanks for the input, its reassured me that one fixture can be enough and two, too much. Despite this, it is quite a deal, and these aren't the highest outputting fixtures from what I read.

Ah, it is quite a bit of money saved if I get one fixture.

And yes I plan on running co2