By the cool looking crabs, you must mean mantis, because they are a big pain, and should only be kept in a seperate environment. You shouldnt risk the chance of the crab making its way up into the tank. The fuge is perfect for pods
and macro, but I must say that theres only one SAFE macro algae, and that is chaeto. The reason why is caleupra and other macros can go sexual and make pollutants into your tank which is very bad for the corals and can kill them. Cheato does a great job of taking out phosphates and nitrates, great place for pods
, grows alot, no special care just put it in the water (it floats sort of). Its the safest macro, I definately recommend it!