Compatible species:
    - Pomacea bridgesii (AKA spike-topped apple snails, AKA Brazilian apple snail)
      are helpful by eating any algae that grows in the pond.
            http://en.wikipedia.org/wiki/Marisa_cornuarietis
            http://en.wikipedia.org/wiki/Apple_snail
            http://www.applesnail.net/content/care.php