Sea slug can mean many things, there are several readily available varietys for the aquarium hobby. The Sea Hare, Cucumber and Nucibranch. All of the mentioned are reef save as a rule. However this does mean that they are fish safe. Regarding the Sea Hare and Cucumber, should they become stressed out or feel threatened they can release an "ink" that is invisible and very toxic to fish. This ink however is harmless to other inverts such as crabs shrimp and corals. Another thing to keep in mind is wether or not they are sand sifters. If they are be cautious. Sand sifters are notorious for over sifting sand and this leaves you with sterile sand. This is bad. They can be very rewarding and a joy to keep. One more thing regarding the Nudibranch. Most are best left for expert reef keepers and should not be kept unless you also use a refugium. They have very specific diets and can be nearly impossible to fee. The lettuce Nudibranch is the only species I know of that can be quite happy in' a well established reef system. If you are absolutely determined to keep one and do not have an attached refugium then you need to feed them cocopods. A very good brand is a product called Cyclopeeze. Your corals with love these cocopods too!!!
