Mix one packet for each cup of tankwater. Put it in a container that will be deep enough to cover your zoanthids. I have several "combo" rocks with lots of different zoas, so I have to use two or three packets. I use one of those disposable fruit salad containers like you get at Meijer Make sure it is well mixed and temp shouldn't be a problem, as you just took it from your display tank. I do six or seven at a time. Put the zoanthids in the mixture and leave them in there for 15 to 20 minutes. Take them out and put them in a rinse container of just tankwater. Shake them off and inspect them for anything else you need to take care of (like algae or whatever) before you put them back in your tank. Treat ALL of your zoanthids. Take six or seven more frags out of your tank and repeat the process until all zoanthids have been dipped. A couple of days later, you can re-treat any that appear to require further treatment in a fresh batch of the Furan 2 solution, but then you should give them a week to recover before any further treatment.
Hope this helps!