You can add crabs to the cuc while still using this ruff forumla, I am not a big crab fan, though fun to watch, they often eat your snails - so if you have snails & crabs, you will need to replace your snails from time to time - keeping lots of empty shells for the hermits to move into as they grow, helps.
Hera an example from John, the owner of reefcleaners for a 90 gallon tank
http://www.reefcleaners.org/aquarium-store/quick-crew-90-gallon
Shipped for free via Express Mail you will get:
85 Dwarf Ceriths - small cleaners that get to the nooks and crannies. Feed on diatoms, cyano, algal detritus, and film algae. Nocturnal cleaners that leave the sandbed at night to search for food.
29 Nassarius - scavengers that will eat leftover food and some fish waste. They will stir sand, but can also be kept in bare bottom tanks.
27 Florida Ceriths - small cleaners that get to the nooks and crannies. Feed on fine hair algae, diatoms, cyano, algal detritus, and film algae. Nocturnal cleaners that leave the sandbed at night to search for food.
32 Nerites - We are currently offering the longer lived and quite hardy Antillean Nerite. (Nerita fulgurans). It grows to a nice size,and consumes a good deal of diatoms, cyano, algal detritus, and film algae. It will also consume some fine hair algae. A nocturnal herbivore that will feed more often at night, they tend to need some time to adjust to the limitations of the aquarium during their first week.