A plankton fiendly tank is one that contains nothing to trap or filter the hatchlings from the water column (no sponges, no corals, etc). Cleaner shrimp are hermaphrodites, so any pair will be fertile and produce eggs. But, in most systems, the hatchlings (free swimming at this stage, do not look like the adult shrimp) are caught by filter feeding corals, crustaceans, and fish, or get trapped in sponges and other fine-particle media, or starve for lack of available food in the water column. So--you seldom will get more shrimp in a community setup.