I started a RCS tank in January and have been selling the shrimplets on my Local Craiglist. I just last month added a few more- purposely from a different source than where I bought my first shrimp. I'm still getting great colors, but just wanted to make sure I kept the line strong with some new blood so-to-speak. Honestly though, I really don't know the correct answer to your question. If you have the room in your tank, adding a few more is going to help the health of your future shrimp rather than hurt them, IMO.