It looks like cyano bacteria to me.
The quickest way to get rid of it is to use some red slime remover. Multiple companies make their version of the stuff, and all of them will cause your skimmer to overflow. Remove carbon, turn off skimmer, and let the stuff do its work for 3-4 days. Afterwards, do a water changes, turn skimmer back on, and add carbon back in.
There are some things you can do regardless of whether or not you use the medication. Increase flow in the refugium chamber, pull the cheato and shake the cyano off into a bucket full of saltwater, and monitor your nutrients. I've read and been told on several occasions that zero nitrate/phosphate environments tend to spur cyano growth. I've been dosing nitrates for only a few weeks though, which isn't long enough to say whether or not it works.