small refugium.. what to go in it?

[asylumdown]

I just received an Aquafuge 2 refugium from CPR Aquatic (the small size from J&L) and I'm wondering what sort of macroalgae I should put in it? My 20 gallon nano has a problem with grape caulerpa that I think would quickly gum up the insides with it's snaky vines, so I'm hoping to grow something that can out compete it.

It's a softy tank and I don't dose any calcium or alk, so I don't wan anything that will require additives.

ETA: I've never used a fuge before, I've also go the lights that come with it and am not sure if I should leave them on 24/7 or if I should have them on opposite the main tank lights. Do different macros require different light cycles?