Hi Allyson;
Ich doesn't effect inverts so no worries about the brittle star. And that's 72 days, not hours, for the ultra fail safe. Does your scooter blenny eat prepared foods? Even frozen or fresh brine? If not, moving him long term to a hospital tank may not work out, he would probably starve.
How badly is the clown affected? Covered with spots or just a few? Is it just the one? If it hasn't taken over the whole tank yet, I'd try feeding them with garlic rather than tearing the tank apart to chase them down and stressing everyone in a small tank. You can get water soluble garlic gelcaps at the health food store, some drug stores and even at the grocery store vitamin/herb section on occasion. Soak the fish's food in that and some Selcon every day before feeding. The ich parasites don't like the smell of garlic fish

and will drop off, be unable to complete their life cycle and will eventually die. There shouldn't be any problem with the clowns eating it, I don't know about the scooter
Alice