In case anyone was wondering, the furan 2 seems to be working. I don't see any spots on the zoas and they're opening up again. I used about 1.5 cups of fresh saltwater and one packet of furan 2. I put an air stone in the mixture along with the zoas and let them sit for 30 minutes. I then dipped the zoas in more fresh saltwater and put them back in the tank. I did this for two days in a row. They started showing improvement after a couple of days. It's been about a week and they've continued to improve.