Multi-stage filter pumps out 925 US Gal (3,500 L) of water per hour, Smart Pump advanced microchip technology continuously monitors and optimizes pump performance Self-starting just add water, plug in and Smart Pump will take over, trapped air auto-evacuated every 12 hours to ensure maximum efficiency Easy water changes eliminate need to lift heavy buckets. Simply attach hosing to output and Smart Pump does the rest Removable, stackable media baskets eliminate water bypass and hold a total of 1.5 US Gal (5.9 L) of media, all filter media included - mechanical, chemical and biological Compact 21 in (53 cm) tall design - easily fits under most aquariums