There is no rule for a cuc but I did 5 hermits and 5 snails. Then a week later a pepermint shrimp and a skunk cleaner. Just make sure you have shells for the hermits or they will kill your snails. But dont add anything intill your tank cycles first. Also Get an emrild crab. Just got one the other day he is the collest thing in the tank. Eat hair alge like crazy.