I must agree, having a quarantine tank is like setting another reef tank, even worst if its a sps tank. Extra money.
Those flatworms are a PIA. Thought of seeing them makes my hair stand even now.
But having those six liner, gobies that supposely eat flat worms would be good. But we must think, if we have high flow that surround those infested acros, no fishes will swim around them. So flatworms will be safe.