[happi]

Thanks for the replies! If I were to go with a 75 gallon planted is there a decent fixture out there? Would 2 of the 108 watt T5HO fixtures be overkill on a 75 gallon? I would imagine I would need something other then 108 fixture as the 75 gallon is a lot wider?

for 75g go with 3x54w fixture, i think 4x54 will be way too much light to deal with. 2x54w light on 75g should still put you on medium light.

 

[happi]

55 gallon - 48x13x20
75 gallon - 48x18x20

The tanks are the same height, so any light that is high light on one is high light on the other. The only significant difference is that the substrate would not be as uniformly lighted on the 75 gallon tank. A very good way to light those tanks is with one 2 bulb T5NO light on the 55 gallon, and two 2 bulb T5NO lights on the 75 gallon, with the lights widely separated. That gives you good medium light for both tanks. Two bulb T5HO lights should be raised about 3-4 inches on either tank, to avoid having such high light that algae is your main concern instead of fish and plants. CO2, not Excel, is a very good idea with any of those light setups.

+1 on what Hoppy said, the 2x54 on 75g wont give you good spread light, it will put more and less light at certain areas in the tank. i never used T5NO so i don't know much about them. the 2x54w could give you medium light on 75g if raised 5-6 inches high from the tank and this will also cover the area where light would not have reached before.

 

[happi]

Happi's advice is good. @ 2x54w - med. light - on a 75 gal. would be just fine, say no more than 8 hrs./day, and you may not need to bother with CO2 - Moderate weekly or semi-weekly dosing with Excel would do the job, IMHO.

you will need to dose fertilizer and co2 under this light, 2x54w on 75g will put you on medium light if hanged above 5-6 inches high from the tank, if it will set on the tank then you will have high light still.