It's good to keep extra shells in the tank to allow clean up crew members to grow, but how many extra shells should you keep? I recently inherited a JBJ Nanocube 28 from a family member and the sand bed is littered with cleanup crew shells over many years. There are currently about a dozen members in the tank (a mix of snails and hermits). I have way more shells than cleanup crew members. Can I remove some of them or do I risk losing some members if they outgrow the available shells?