planeria, the red flatworms you have are killed by flatworm exit...you might have to go up on the dosage but it works.. i was unfortuante to get these when i picked up some sps on a trade 2 years ago.. i did a whole series of tests of how to get rid of these guys, flatworm exit, intercept, metronidazole, ketoconazole, amoxicilllin,and potassium permanganate. Your right what you say about harm, but not a single hermit or snail were killed when i dosed my tank. i did lose a barlet anthia (but i also dosed intercept at the same time, so i dont know which one was to blame), but thats it, no urchins, no starfish , nothing. Nothing but potassium permanganate works better then flatworm exit. Permanganate not only kills the flatworms but also thier eggs.. something that the flatworm exit does not. But you cannot use this on anything but corals.. fish and inverts WILL die.. i have dipped every coral i have got since that episode in a flatworm exit dip for 10 mins, i have not lost a coral, nor have i had planeria come back... just my 2 cents.. im sure others can chime in on thier experiences.. But i do suggest if your gonna dose the tank with chemicals , please talk to someone that has done so before to guide you,,, now if you have acro eating flatworms, thats a different ballgame, and flatworm exit is questionable in its ability to rid your tank of these guys...