Yup, I agree. If you just take out some fish, the parasites will hang out on the available fish, then reinfect the clean fish as soon as they are back in. However, it shouldn't be too expensive to buy a few 10g tanks (a few 10g are cheaper than a 20), some sponge filters ($5 a pop), heaters and an airpump and keep the fish all out of there. Certainly cheaper than buying all new fish... Or, just check craigslist or something and get a cheap 55g, and do teh same with a few sponge filters.
Good luck and keep us posted--
Christine