For large ponds up to 12,000 litres (2,640 gallons).Fantastic value - this filter comes complete with a powerful 18w UVC and comprehensive filter media. At last a genuine multi-chamber professional filter box that anyone can afford. We feel sure that these new units will prove a hit. Dirty water enters through the multistage hosetail past the UVC where it is pushed through foam into the first chamber of biomedia. The water is then flows into a second chamber and is forced upwards through the foam up and over into the final chamber. Clean water then returns. NOTE: UVC bulb included.