Sorry I am new to these forums, so just thought I would chime in on here with a recent experience...
My 55 gallon mixed reef developed a flat worm problem a few weeks after a frag swap I attended, all my corals from the swap appeared clean, so I assumed they were eggs when they came in.
They quickly populated my tank. I attempted Blue lifes Flatworm control, with no effect at all on the flatworms. <I like to try new products, sometimes that is the results>
My wife said she wanted to redo the floors in that room, so I figured tearing down the tank was a good time to treat it, so I borrowed another tank from a friend, and I freshwater dipped all of my rock going into the new tank, and put all my corals infront of a powerhead for a few seconds.
This knocked the flatworm population going into the new tank down a ton. Then I treated the new tank with a double dose of Salifert flatworm exit. The remaining flat worms pretty much dropped dead with in minutes.
When the floors were done, I moved everything back to my tank, and got it all set back up and hit it with another double dose of flatworm exit.
It has been almost a month and I have not seen a single flat worm, and I have another bottle of flat worm exit sitting here just in case. I figure if any eggs survived, I would be ready to hit them as soon as I see them to prevent a reoccurance.
Someone mentioned their local store was battleing flatworms, I got this idea for treatment from a local fish store when I helped them do the same thing to the SPS display tanks.
However if you see a coral you must have at that store, take it home, put it in a gallon jug of saltwater, use a double dose of flat worm exit, then after a few minutes put it in another bucket of saltwater and slosh it around a bit. You should be ok at that point, but if still concerned set up a QT tank, I told myself I would,, and I still haven't.