I think I've figured it out...more googling has me thinking that it's red turf algae
, which, according to some folks
, thrives in clean water.
It looks to be slowly spreading over the piece of live rock that has my zoa colony, so without killing the zoas, I can't do anything suggested here: Progress on Red Turf Algae | Living Reefs
Would either a tuxedo urchin, or mexican turbo snail be appropriate in a 20 gallon nano? More importantly, could either of them manuever through the zoas to get to the stuff, or will they kill the zoas? I have other algae on the glass (nothing major, just the typical junk that needs to be cleaned off weekly) that it could feed on as well.