I wouldnt use chelidonura varians, I say this because I did. The slug didnt last very long and I was left with flatworms. Saliferts Flatworm Exit (FWE) has worked for quite a few people, I have used it and still had flatworms. Also FWE is indiscriminate and kills beneficial flatworms as well, and does seem to have a bad effect on other beneficial invertebrate life. I will never treat my display with it again. If kept under control with regular siphoning the flatworms pose little or no threat to the other life in your tank. However if they are allowed to go out of control they can cover corals and effectivly block light, and if the flatworm population crashes all at once the toxins they release when they die can nuke your tank. This is also a concern when using FWE, be sure to follow the instructions closely if you decide to use it.