Tetra Pond In-Pond Skimmer is designed to remove debris from the water's surface before it sinks, acting as a pre-filter and helping protect your pump from clogging. Water and debris are drawn into the skimmer, and debris collects inside. Water is drawn into the pump, then discharged to an external filter or waterfall. Use with large flexible or pre-formed ponds that are 500 to 1,000 gallons. Tetra In-Pond Skimmer is easy to install and clean and comes with complete instructions for setup. The skimmer should be installed on a pond shelf or on blocks - built with four corner pockets that can be filled with sand or gravel to prevent the skimmer from floating. Contains a basket to collect large debris and a filter pad that collects smaller particles (replacement pads sold separately). The floating weir door maximizes surface cleaning. Includes a 2-year limited warranty - see packaging for details.