If it were me in your situation, this is what I would do...this is me only. Others will have their opinions, and just to be fair, there are many different ways to fix this. It just depends on your desire, financial situation, love of your fish, and time you are willing to invest in the hobby.
First, read up on ick. There are some really good sticky threads on Reef Central. Ick is a parasite. It never goes away once you get it in your tank, unless you take your fish out of that tank and let it sit fishless for 72 days. No less than 72 days. I have seen fish go back in at 60 days and get ick all over again. Some will just say to keep your fish healthy by proper feeding and water quality and they will be fine. That obviously works for them and that is fine. I am too anal. Of course I am the same person that quarantines live rock, coral, inverts, and of course fish for 3 months before they go into my DT. If they can't survive my quarantine process, they don't get to see the DT.
You haven't mentioned the size of your fish so I will assume they are relatively small.
I would get 2- 20 long tanks from petco, an air pump, several air stones, and a couple $10 hob filters. Do the tank transfer method (spelled out on threads in here and on RC) and then transfer them to a final tank that is large enough to house them for the duration of the 72 days while your DT sits fishless. Put something over the top so they don't jump out and put something in there like some PVC fittings for them to hide in. Be sure to keep the tank aerated discarding the air stone with each transfer. Get an ammonia test kit to test ammonia at least once (preferably twice) a day. I don't use nets to transfer the fish but rather a colander. Also get a couple of 20w heaters. I like the preset ones from petco. Clean and sterilize everything between transfers. One is cleaning while you are using the other. No water of any kind gets switched from one tank to the next (except for the water on the fish).
Set up the third tank and have it cycling so that it is ready when the transfer method is finished. Make sure that nothing from your display tank goes into this tank. No water, no rocks, no sand, nothing.
Finally, I would get some cupramine and have it on stand by in case the ick gets so bad that the transfer process isn't working. That imo is a last resort.
Read up lots but don't hesitate in getting started as time is a serious factor in any parasite outbreak. If you start now, the chances of saving your fish are 99%. If you want me to walk you through it on the phone, pm me and I will send you my number.
