Treat ALL the fish you have and leave the tank empty of ANY fish (new or old). The shrimps are fine, and they won't survive hypo anyway.
After the fish are treated and the tank has been empty, put the fish back in the main tank. Clean and bleach the QT and restart it. You are now ready to get new fishies -- place them in QT for 4-6 weeks, and possibly perform hypo as a precaution. Time in isolation seems cruel at first, but it is really a quiet time to get them used to captive life and prepared foods.
When you get fish, look around the store. See any fish with ick? Then likely your new guy has it, too, and should be treated with hypo. Tangs, always. In 4-6 weeks you should see signs of ick on other fish if you watch carefully.
Don't mix any new fish with your current fish in QT. You could end up with an ugly disease smorgasbord. If you see something you can't live without, you can always start a second QT, but absolutely don't shared anything wet (including your hands! scrub well!) between the tanks.
It's important that nothing, no a droplet of water, come from your QT into the main tank and vice versa during the QT period.