Too many questions in my mind about possible interactions that FWE may have with other creatures in the tank, not to mention the toxicity of the flatworms as they die. Although many people have used it with success I am not one of them, the flatworms always come back, but that was a long time ago and I refuse to use it now. I did try Chelidonura Varians aka. Velvet Nudibranch, it certainly had an appetite for them as suggested, but disappeared after about a week never to be seen again. I would not recommend them for this purpose. Some Damselfish are reported to eat them as Justin suggested, and I have witnessed my Clarkii clownfish eating them, however my green Chromis doesnt. Now I just keep their population as low as possible with regular siphoning at water change time. I have read that thier population will eventually crash. The reasons for this seem to be unknown so I'm keeping my population low and hoping for the day when this happens.