There are so many different types of filters out there that do such a variety of different chores, we have divided them into easy to follow categories. We have In Pond filters that are designed for smaller applications. These are usually reserved for the ornamental garden with a very light fish load. Next, we have pressure filters. Pressure filters are also for a light fish load, but are designed to be placed outside of the pond where you can backwash them, and placement can be away from the pond for a clean aesthetic look. Mechanical pond filters are just that. They are for a heavier fish load and really "clean" the water. Waterfall filters combine filtration and oxygenation for smaller applications. We recommend them for small water features, streams, and some pondless systems. Biological systems usually combine some sort of a mechanical system and media to create a surface bed for beneficial bacteria to grow. The beneficial bacteria clean the water simply by living on these surfaces. We highly support the use of biological filters in many applications. Sand filters scrub the water, are a bit higher on the maintenance curve, and do an effective job purifying water, but are not for every application.
You're sure to have questions, so please feel free to call one of our customer service reps, and we'll be glad to lend a hand in any way we can.