Greenstop 72W uvc clarifier
This is a serious piece of kit at a very realistic price. This large chambers of this UV unit (Just under 1m long, 3' 3") allows plenty of time for your pond water to be exposed to UVC radiation.
The chambers also incorporate a helix meaning that the water turbulates through the chamber increasing the level of radiation exposure.
Helix water disturber.
2 x 36 watt power.