Up to 1000 gallons. Maximum Flow of 1000 gph. The Ultima II is specifically engineered to meet the environmental demands of fish ponds. It uses tubular Bio-Media designed for high flow rates. Media comes in three different sizes with random lengths and diameters to avoid stacking. A patented backwash system keeps the media from clogging. Cleaning the filter is done by internal jets. The Ultima II is also the ideal filter for aquariums where very high flow rates are desired. The Ultima II is available in large industrial sizes. 1.5 Inch inlet/outlet(product code: AU50073)