With Angels, I'd run Cupramine at .35ppm. Angels are copper-sensitive and Cupramine is very effective at this level. I'd skip the Selcon for now. Its great stuff, but its benefits are long-term. The fish won't be missing anything for the short time in QT and you're just adding another pollutant. Most ammonia test kits don't work with copper, but the stick-on badges do. Monitoring ammonia in a QT is vital. You can't "just not worry about it for 21 days". Unless you had a way to cycle the QT, ammonia will need to be controlled with very regular WCs. Do not use any of the ammonia neutralizers (Prime, Ammo-Lock, etc); they form deadly compounds with copper.
BTW, are these newly purchased fish and what are you treating for: Prevention or parasites?