The Superfish TopClear pressure filters are a unique 3-step pond pressure filter. First of all filter foam provides the mechanical filtering, which removes larger particles and debris from the water. Then in the second step bacteria in the bio-balls provide the biological purification to break down waste products. Finally a built-in UVC steriliser provides control of algae and works to prevent against diseases. 
 
Superfish state that if added to an existing pond the built-in UVC, clarifies your pond water within a fortnight. The external top mounted UV indicator in the lid means you can easily check whether the UV lamp is on without having to open the unit. Also included is a flow indicator which shows the flow rate, so you can see when the filter needs cleaning. Cleaning is made easy thanks to the auto clean wash function.