Is this killing my sps?

[Myka]

F.H. is right, those buggers are terrible. If you can easily replace these Montis (the ones you mention are common), I'd pull them all out of your tank and throw them in the garbage. You probably have them growing on the rocks, and those bits you probably can't remove. Once the Montis eat all the remaining bits, then start your countdown - a couple months without Montis should be fine. Their life cycle is less than 2 weeks, so if you wait 3-4 life cycles you should be plenty in the clear.