return pump, skimmer, cheato, rubble rock, cerith snail, hitcher stomatella snail, isopods, amphipods, copepods, and the itty bitty peppermint shrimp now more than 2 inches long, sand, bristle worms, spagetti worms, chemi-pure elite, um ........ other critters I am sure. My sump isnt large enough for my heater or else it would be down there as well.