Frustrated with disappearances 10/25/05
Good morning. 
<And to you> 
I'm a new hobbyist, and have learned a great deal from your website, but was wondering if you could help me with a frustrating problem. I've followed lots of advice from your site, and after about 6 weeks, I have the beginnings of some nice coralline growth on my live rock. My problem is disappearing bottom feeders, specifically a 3.5 inch algae blenny about two weeks ago (never found a trace, in spite of moving around rocks), and now a new 3.5 inch sand-sifting orange spot goby who looked great sifting my sand bed yesterday, and then just vanished. It's only been a day, but I fear the worst. 
I have a 36 gallon bowfront, 4" deep sand bed (Caribbean play sand), 10 pounds base lace rock, 40 pounds mixed Florida and Fiji live rock, 2 internal powerheads, hang-on Prizm skimmer, hang-on filter (for intermittent charcoal and mechanical filtration), 2 65Watt power compact lights. Ammonia, nitrites, nitrates undetectable. pH is 8.2 and temp steady around 80. Occupants are 2 true percula clowns, one small coral beauty angel, 1 brittle star (definitely not green), 1 common cleaner shrimp, 8 blue leg hermits, 3 red leg hermits, 5 Astrea snails, 5 Nassarius snails, and 2 small emerald crabs (roughly ¾" across the shell). 
After reading your site, my suspects are:
1: hidden predator (unseen Mantis despite prevention attempts, and not seeing anything staying up to watch at night) or...
2: the emeralds.
3: brittle star.
I was hoping you could help with my suspect list, and advice/course of action to find the culprit. I'd be surprised to hear the emeralds or brittle star are at fault given the size of them in relation to the missing fish, but I'll defer to your experience. I would really like to get on small bottom fish (preferably a goby or Jawfish), but I'm frustrated with the losses (and the cost), so I don't want to add anything else until I've sorted it out. I don't want to remove all the rock, so my thought was to proceed with some sort of trap at night. I'd love to tap your experience on:
1: Am I on the right track in assuming I've got a mantis, or would you suspect another culprit?
2: How common are mantis shrimp? I've read about them at your site, but everybody at the LFS said they had never even seen a mantis shrimp. How unlucky could I be with such a relatively small amount of rock?
3: What to do about it... I've considered fashioning some type of trap and baiting with shrimp, but I'd like you advice on where to place it and what to bait it with. With the type of fish disappearing, I'm unsure whether to trap near the rock, or along the sandbed in the front. If there's a bad guy in there, I suspect he's buried in the rock, and traps the fish when they are either sleeping or foraging deep in the rock. I've had no trouble (at least not yet) with the coral beauty, or the clowns.
Thanks for a great site!!!! I'm loving the hobby so far, but this particular frustration is really giving me a fit (and my little boy gets really upset when we lose a fish)....
<Unless the brittle star is fairly large, it doesn't appear you have any threat to your fish. Getting mantis shrimp as hitchhikers in live rock isn't that uncommon. Do you ever hear any clicking sounds at night? Are you sure the fish aren't in a overflow box etc? Did you check the floor behind the tank? If everything is OK in that regard, I'd probably get a mantis trap and bait it with some frozen type of food. The orange spotted gobies do best with a live sand bed and frequent feedings. Quite possible he wasn't getting enough food and may be dead and buried in the sand bed. Try stirring up the sand and see if that isn't the case. James (Salty Dog)>