macroalgae, sorry...there are many different types like grape caulpera, chaetomorpha, red hawaiian...etcetc...basically helps take out certains things like nitrates and what not, be careful on some, like the grape...as it can go sexual and kill your whole tank....maybe people have it in their refuges.....i'm sure if you do a search youll see tons of info.....what are you plans for the intake refuge?? if it just is holding live rock...wouldnt it be the same as putting it in the tank on the sand somewhere, give ya more room for other rock etc? or were you planning on something else with it?