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Ultra Violet Sterilizers

One of the most important pieces of equipment for any Koi Enthusiast, unless they particularly like 'Green Water' and don't wish to be able to see their prized possessions, is....

The Ultra Violet Sterilizer !


Single-celled green algae require light and nutrients to thrive. Sunlight, unless the pool is in a shaded spot or protected by a pergola or overhanging plants, works with nitrates to bring on bloom, sometimes in a matter of hours. The small diameter of the Chlorella vulgaris cells means they can pass through all conventional filter media and all but the finest open-celled foam, so physically filtering them out in their normal form is next to impossible unless the medium is partially blocked. However, passing the cells through a UV disrupts their internal structure, if not actual killing them, so that they clump together or 'flocculate'. These clumps, being of a relatively large diameter, can be trapped and broken down by the filter.


Most Koi keepers will keep their unit(s) switched on 12 months of the year. But the owners of small garden ponds may just find that only in the spring, with the combination of longer days and an upsurge in fish activity (and, therefore waste production) is UV necessary. If you intend to run your UV year-round, it must be protected from frost in a well-ventilated housing. Again the recommendations vary depending on the manufacturer, some suggesting that the unit be dismantled and stored dry over winter.


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. However, this is an oversimplification. Pond capacity is not the only factor to take into consideration - stocking levels, how much sunlight the water receives and the amount of shading will determine which size UV is right for you.


Obviously, for maximum efficiency, you should run our UV in conjunction with a pump rated in gallons per hour to suit the size of your pond. The longer the contact time of the water with the UV light, the more algae spores will be treated, but there is a lower limit to the throughput of water, beyond which filter efficiency and/or aeration via the Venturi may suffer. If your pond has only on UV and one run of return pipework, you may have to compromise, on the basis that the pump must circulate the entire pond volume once every two or three hours (as an example, a 1,000 gallon pond should be teamed with an 8-15 watt UV and pumping rate of 500 gph minimum). One way of irradiating a large pond with only one UV is to T-off some of the flow through the unit. This treated water need not necessarily be returned direct to the main body of the pond - it can be diverted back into the filter. If you have two UV's plumbed in parallel, servicing the same pond, you can effectively double the contact time in each UV unit and substantially increase the amount of irradiation. The latter is a useful option in very large ponds, and manufacturers may offer tandem conversion kits, enabling you to 'bolt on' one or more UV's.

Bearing in mind what we have mentioned above - Using the correct size U.V. not only  clears 'Green Water' but also enables you to be able to view your Koi in Crystal Clear Water, and as the term 'Sterilizer' infers, it also sterilizes the water itself - thus helping to kill the harmful Bacteria that lives in the water and which cause problems to our valuable Koi - So a correct size U.V. is beneficial all round.

Using any U.V. not only  clears 'Green Water' but also enables you to be able to view your Koi in Crystal Clear 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 and which cause problems to our valuable Koi - So using the correct size U.V. is beneficial all round.

At THE EAST RIDING KOI Co. we use and recommend the U.V's marketed under the Brand Names of 'YAMITSU' and 'POND-CLEAR'' - both of these manufacturers have an excellent reputation and their products are both reliable and well made - there are of course many other manufactures who all produce 'Good & Effective' U.V's which we will obtain for you if you would prefer them .... Just let us know what it is you want .... OK

The U.V's come in various Sizes - From just 6 watts right up to 240 watt. The size you require depends on the amount of water in your pond or tank.

In The Yamitsu Range:

As a guide: 10 watts will be sufficient for a pond with 1,000 gals - 60 watt = 6,000 gals, so you can work it out from those examples on what size of U.V. you require. The Yamitsu range covers UV's from 6 watts right up to 240 watt.

In The Pond Clear range

Providing we are talking about a correctly filtered 'True Koi' pond - then, again as an example, the 55watt U.V. will adequately cope with a pond up to a maximum of 10,000 gals. Pond-clear do manufacture smaller units.


And as you would expect: we keep a full range of spare 'Tubes' and certain other spare parts.



Please contact us if we can help in any matter <sales@koicarp.net>