Submersible UV Clarifier
If you have trouble hiding a UV clarifier or keeping it out of the weather then the new Pondmaster models may be just what you're looking for. From Danner Mfg. suppliers of pond and watergardening products comes a UV clarifier design that is quite revolutionary in that it's the only one that's totally submersible.
It can be positioned like any other UV lamp but there's no need to worry about weather protection or splashes from the pond. This gives great flexibility for design within your koi pond especially one built at ground level. It is also very suitable for connection to a submersible pump with less pipe work needed. The pond pump and the UV clarifier could be placed together in the end chamber of a gravity fed filter, out of sight and without any electrical safety worries.
The Pondmaster UV comes in three different sizes with the largest having a 40 watt lamp and is suitable for a pump rated at 3000 US gph. All three are supplied with a 900 hour long life lamp and are a vortex design to maximize water contact time. The black colour and slim design means they can be hidden within a pond with a clever halo ring to tell you it's on.