In my experience, garlic works wonders when it's not advanced (I've never yet had to treat an advanced case).
Sk8r's advice is sound, but the disruption and available resources may make that approach less viable (catching a hippo tang with available hiding places is no easy trick, and that's just one fish). If you dose heavily with garlic and see improvements in a day or two you might get away with it. But those parasites will be around for weeks, so you will have to keep treating with garlic and probably also vitamin supplements since your only defense will be healthy immune systems until all the parasites are dead or dormant (I seem to recall they have an encysted state so they can come back later, but I may be confusing them with another organism).
But to be sure, the quarantine and hyposalinity is the approach that will give you more chance for success and mitigation of losses.
If you use garlic in the future once this outbreak is over, and keep other conditions good, you shouldn't have a problem again.
Brad