Advice for a newbie with a marine tank

[Martmanicus]

I found a great reference site for just this thing
http://ozreef.org/library/articles/mantis_shrimp.html

Wow you know he's attacking every snail in site. I moved a bunch of snails off that piece of rock and yet I can still here him every minute or so whacking something else. Violent little buggers. Yeah I read that club soda is some kind of awful for them.

I don't want to kill him but I"m afraid I don't have much choice as I don't have a sump and I'm sure nobody wants to come pick up a homicidal mantis from downtown Vancouver

I don't know what type of crabs they are. It's Indonesian rock appearantly. The crabs are also hiding out in a bunch of holes. I piked several pieces of live rock that are riddled with caves thinking they looked interesting. After reading about mantis shrimp I think that all the caves have been dug out by them. Hopefully there is only one of them in my tank.

So after I'm done I'm just going to rebuild my aquascape ontop of the sand. Is this a bad idea? I don't want to disturb the sand too much as it took quite awhile for the cloudyness to go away and I can't drain my tank this time.