I'd probably add a few more snails, but keep inmind that different snails behave and act differently and will have different foods sources, what exactly are you needing clenaed? Glass covered in algae, hair aglae on the rocks, cynobacteria, diatoms? All depends on what you need accomplished. A variety is always better IMO. Also, don't plan on the hermits really doing much "cleaning". Their opportunistic feeders and will feed on whatever they can get their grubby claws on.