Blog | Water Garden Ltd - Choosing a Pond Filter System

Choosing a Pond Filter System

28th July 2012
Choosing a Pond Filter System

Selecting the right filter for your pond can be a confusing task, so over the next few posts we’ll discuss why and what you need to keep your pond in tip-top condition, all year round. 

Firstly, why do you need a pond filter?  Any body of water which is exposed to daylight or sunlight is likely to go green and murky.  The green water is caused by single-celled algae which breed very rapidly during the warmer months.  In addition, pond debris will also end up sinking to the bottom of the pond (leaves, pollen, grass clippings, fish waste etc.) which add unwanted nutrient into the water.  Unless you particularly want the ‘green and grim’ look, the best bet is to install a pond filter system!  Also view our Pond Filters Selection Guide for useful tips.

There are three main parts to a pond filter system:   

1. Solids-handling Pump

2. Ultraviolet Clarifier (UVC)

3. Mechanical/Biological Filter. 

The purpose of the pump is to circulate the pond and also to supply the water and debris to the filter.  The filter pump must be able to pass solid waste, so it’s important to select a good quality ‘solids handling’ pump.  OASE manufacture the best pumps on the marketplace today and these offer reliable, consistent performance.  You can read more about pump selection on our Pond Pumps department here.

The UV Clarifier (also known as a UVC or ultraviolet clarifier) is specifically designed to tackle the problem of green water.  The UV radiation produced will cause microscopic algae to flocculate (clump together), which can then be trapped in the mechanical and biological stages of the filter.  Single celled algae is too small to be trapped by a filter and would simply pass through the system, hence the need for the UV Clarifier.  The UVC will also kill off harmful pathogens and other nasties in the water.  See our UV Clarifiers department here for more details.

The Pond Filter serves two functions.  Firstly, the mechanical stage of the filter will physically trap pond debris and flocculated algae passed from the pump and UVC.  The mechanical part of the filter usually uses special sponges (coarse and fine) to trap the debris and these have a very large surface area to reduce the need to clean the filter frequently.  The biological filtration stage usually consists of either sponges of special filter media which ‘friendly’ bacteria can live and breed on.  This vital bacteria will help to break down waste matter trapped within the filter.  View our Pond Filters department here for more details.

Although these 3 parts can be purchased individually, its far simpler (and generally cheaper) to buy a filter kit which contain a pump, UVC and filter.  These sets have been optimally matched to suit the specific size of the pond.  Make sure that you account for fish stocked in the pond, as these will put additional strain on any filter.


In our next post, we’ll explain how to measure your pond and also discuss ‘all-in-one’ filters for smaller ponds and water features.

Feel free to contact Water Garden Ltd for more advice or guidance.  Call us on 02392 373735 or drop us an email – we’ll always do our best to help!

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