[Stargazer]

Here's another lighting question but I'm just not sure if this is enough. Recently set up 75 gl with 96 watt cf and a 32 watt normal fluorescent. Some of the plants are Rotala wallichi, Blyxa japonica, Rotala Macrandra green, Limnophila, Hygrophila Corymbosa, Lindernia rotundifolia variegated and a few others that I picked up yesterday locally that I have not identified yet. If needed I have a 48" double T5HO that I could use in place of the 32 watt fixture.

 

[FSM]

I would put the T5HO fixture on it.

 

[captain_bu]

You certainly don't need two fixtures. Either use the T5s or the CF. Each would be a good choice. The T5s will give you more light, probably keep your wallichi happier, the rest of the plants on your list are pretty easy plants to grow. A 75 is the same height as a 55 just deeper front to back so a good spread of light is more important than additional intensity. Depending on the design of your fixture your T5s should give you better spread than the CF. Are you using pressurized CO2? It would be a good thing to have with either light, pretty much necessary with the T5s unless you hang them.

 

[Stargazer]

I am using pressurized CO2 and ferts. The cf is a Coralife and the T5HO is a Current. Using only one would give enough light for the wallichi? I thought that was a high light requirement plant and using the T5HO would only be 1.44 wpg even though I guess that really doesn't seem to have too much meaning anymore.

 

[FSM]

Maybe use the T5 for around 8 hours and the PC for a few hours in the middle.

 

[captain_bu]

As you noted the original wpg rule doesn't apply to T5 lighting or CF. The volume of a tank isn't as critical to determining light intensity as the distance from the bulbs to the substrate. The deeper the tank front to back the more bulbs you need for coverage.

I was running a 130 watt CF fixture over a 50 gallon long tank (about an inch shorter in height than your 75), I upgraded to a Catalina 4x54 T5HO fixture and have no need for all four bulbs. 108 watts of T5HO seems at least one and a half times the output of the 130 watts CF. I ended up having to hang the fixture to get better light control, even the two bulbs throw out a lot of light.

 

[Stargazer]

I switched the lights out tonight and have just the T5HO on it now and what a difference. Looks much brighter and is a whiter light which I find nicer looking. Using 10K bulbs.