Lorraine is right, the BSJF isn't part of the CUC. You want critters that roam the tank and BS's stay mostly in one place. I like snails mostly for the CUC. There are dozens of threads on CUC's here. Nassarius, Cerith, and Astrea are the three I recommend most. One per two gallons is my rule, but I may adopt Lorraines one per one....I like inverts!. Just make sure there is enough food for them. Start off light and add more if you need them.