 Re: Who's the culprit
It's possible that you are missing something in your list of creatures. I have often had very dangerous things in my live rock (mantis shrimp). In fact one actually eat an entire medium sized blue tang. Anyway, if you don't see any problem during the day, then my guess is that it is something like a mantis shrimp at night. The only real way to check it out is with a flashlight at night. You will see all kinds of things that you didn't know were there. If you do have something that needs out, you can set a trap for it, but it is somewhat challenging. If you do need to trap something I'd imagine that there are threads here describing how to do it. If you can't find one, let me know and I'll explain how to do it.
Good Luck,
Aaron
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55 Gallon Attemped Reef - 20 Gallon Sump - 250 Watt MH - True Perc, Yellow Tang, Purple Chromis, Snails, Hermits, Sally Lightfoot, Green BTA, Colt, Xenia, Flower Pot, Green Star Polups, Assorted Mushrooms, Maxima Clam, Still Hooked... | 
