It was Erythromycin, which is just an anti bacterial medication, the same thing you get 90% of the time when you visit a Dr. Yes I really wish the skimmer was running to break it down as it dies, most of the cyno is gone now after just about 20 hours, but the skimmer still can't be turned on lol. Just leaving it off for now, all looks well in the tank, the Xenia usually let me know instantly if something is wrong.
I use the meds in freshwater planted tanks to get past the initial red slime outbreaks, and it has worked really well and never comes back, so figured I'd give it a go in my reef.