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  • Posted on: 3/5/2010 12:53
UV and Biological filter? #1
How does a UV and filter work?

If you have a pond and the water turns green people will say get a UV and filter but what are they and what do they do?


UV stands for ultra violet (light) some people call them a UV steriliser, this is wrong as you will see.

The UV light is produced by a fluorescent lamp. As water and electricity don?t mix the UV lamp needs to be in a tube that lets UV light through, ordinary glass stops UV light, so the tube in a UV unit is made from quartz.

The pond water comes in from one end / side of a UV and passes all around the quartz tube getting exposed to the UV light. Varying designs of UV are available, some have spirals to make the exposure time longer.

What Happens

The UV light causes the micro bacteria in the water to flocculate (Clump together) these clumps pass through the UV where they are collected in the filter.

Below is a sketch of a typical UV

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(click to enlarge picture)


The filter serves two purposes. Biological and mechanical.


The mechanical aspect of a filter is to remove any debris the pump sent i.e. parts of leaves, tiny plants, fish waste etc The mechanical side does this by a variety of means (Dependant on manufacturer) Some have brushes, but most use filter foams of varying sizes / shapes.

Below you can see a basic version of a typical box filter. The water enters via a ?spray bar? to evenly distribute the water, then any debris (including that from the UV) Is trapped in these layers.

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(click to enlarge picture)


Below the sponge layers is the filter media, again these will vary according to the maker of the filter, but they all do the same thing. The media has a very large surface area, for ?good bacteria? to colonise. In short the bacteria make the water suitable for fish to live in again.

The water then returns to the pond, again how depends on make of filter.

Not Mentioned. But worthy of note:

Biological filters should be left running 24/7-365.
The good bacteria multiplies over time, a new pond and new filter has no bacteria.
Filter sponges should be cleaned in a bucket of pond water. Tap water will kill bacteria.
The filter and pump should be a suitable size for the pond and its inhabitants. (Koi require a lot more filtration than most other fish)

The UV lamp should be changed once a year, usually at the beginning of the season. (It can be switched off and removed at the end of the pond season)

There is more to a pond, how it works how to look after it. Please look out for other articles for your guidance.