Well it depends. If you used uncured LR to cycle the tank then will be some stuff for a cuc to live off. Generally I recommend holding off on a cuc for a few weeks. Get some livestock (1 or 2 fish) in there for a week or more before getting a cuc. Then start with just a few items (snails) and build up the cuc as the tank matures and the bioload increases. Don't buy a full tank cuc package on day 1.