Believe me , you need snails ! ...and about a 100 of them too ! I know that the are expensive but you need them. well, you might wanna do what i do. when ever i hit the beach i bag'em. Crabs ? not really ; due to the fact that you have a tang that does the same thing he does . Now about the divider ...... no need to go that route ; plus it looks tacky ! Just add more live rock or base rock and make alot of caves. well ima end it on that note and i hope & pray everything goes well ! keep in touch!