What's the difference between a UV Clarifier and a UV Sterilizer?
UV-Clarifiers are used to kill algae along with some disease organisms. The water flows through UV-Clarifiers faster than the UV-Sterilizers.
UV-Sterilizers kill 99% of floating algae as well as other living organisms. They do not harm the beneficial bacteria that grow in filters and on rocks, etc. in the pond. They kill the organisms that are floating in the pond water.
For Koi keeping it is best to opt for a UV sterilizer because it not only clears 'Green Water' but, as the term 'Sterilizer' infers, it also sterilizes the water itself - thus helping to kill the harmful Bacteria that lives in the water.
How does a UV Filter clear green water?
Single-celled green algae, (Chlorella vulgaris) require light and nutrients to thrive. It is one sign that your pond is generally healthy, and it even makes a great food additive for farm animals, but it doesn't do much for your overall enjoyment of viewing Koi!
The small algae cells can pass through all conventional filter, so physically filtering them out in their normal form is next to impossible. However, passing the cells through a UV disrupts their internal structure, if not actually killing them, at which time they clump together or 'flocculate'. These clumps can then be trapped and broken down by the filter.
When to use a UV:
Most Koi keepers will keep their unit(s) on year round. But for small garden ponds you may find that only in the spring, with the combination of longer days and an upsurge in fish activity, is UV necessary. If you do run your UV year-round, it must be protected from frost in a well-ventilated housing. Remember it is important to replace your UV lamps annually for peak performance.
How much UV do you need for your pond?
Purely for green water eradication, 8-10 watts per 1,000 gallons is usually recommended, but some pond keepers will maintain that, for a reduction of bacterial levels, this can be increased threefold to 30 watts. Other factors to consider are of course flow rates, and stocking levels.