My pond water murky cloudy

At some time we are likely to have asked questions such as ‘ How do they keep their water so crystal clear?’ or, ‘what are they doing that I am not?’ when we have seen truly clear water.

Some of the most impressive koi collections I have seen have been made even more stunning by the sheer clarity and sparkle to the pond water. I think that probably most of us at some time have been proud of the clarity of our pond water only to visit an even clearer pond, where it may be 6 feet deep and yet it is still possible to read the manufacturer’s name printed on the bottom drain!

What are the secrets of achieving crystal clear water and is such ultimate water clarity within the grasp of any koi keeper?

Let’s consider what causes cloudy water. Most instances include where we can still see the pond bottom, but it is has lost its sharp focus. It is that elusive final 10% of clarity that is so difficult to achieve and yet well worth the effort when considering the overall final effect. Assuming that the water turnover rates and the removal of solids from the pond are adequate, there are a number of likely causes of cloudy water to be addressed.

1. New and Unbalanced Pond.

A new and unbalanced pond is more likely to have a clarity problem for several reasons and the obvious one is poor water quality. New ponds are often overfed or overstocked before the biological action of the filter has fully matured, leading to an inevitable nitrite problem. A nitrite reading is frequently accompanied by milky water and a sudden deterioration of visibility should be an indication that the water needs testing. Nine times out of ten, having solved a nitrite problem, the cloudiness disappears as well.

Another reason why the water in an immature system may not be so polished is that the media may still be too clean and will not be trapping the microscopic particles effectively. When bacteria colonise filter media, they produce a sticky, slimy substance called zoogleal film, which can inadvertently and very effectively polish the water by trapping and removing tiny particles. This action is very limited in a new pond and filter.

2. Green or Brown Pond Algae.

Excessive algae growth suspended in the water can make the water resemble pea soup. A guaranteed solution to this problem is to install a UV clarifier fitted inline between the pump and filter. If a milky hue returns to a pond while using a UV, it may indicate a number of problems:

a. The UV tube is coming to the end of its useful life and needs replacing (usually every 12 months).

3. Food can cause the water to cloud or change colour.

Water can become cloudy having changed diets or brands and if this is the case, it is quite reasonable to assume the food has been the cause.

Food-related problems may arise from poorly bound ingredients breaking up once the food hits the water or may be caused by the subtleties in the way koi digest a particular diet. Further problems can occur when water becomes discoloured through leaching of food dyes contained within certain diets. This can lead to the colours of the koi appearing to change (particularly whites) and the overall clarity of the water to deteriorate.


The solution to improving clarity where turbidity has not apparently been caused by poor water quality or algae is to enhance filtration and particularly mechanical filtration.

The most common, limiting factor of a filter is its ability to remove solids. A filter is likely to be tested to its limits when fish are feeding actively in the summer. This is why ponds are at their clearest in the winter. If a filter is unable to remove even the smallest of solids then crystal clear water will never become a reality.

Ways of enhancing solids removal.

Solids can be removed through settlement, entrapment in brushes, foam and matting and by changing the flow patterns within a chamber to encourage solids to drop out using a vortex or weir/baffle boards.

Mechanical filtration can be improved by increasing or adding any of the above or by using additional systems.

A very effective way of polishing water to produce crystal clear water is to use a sand pressure filter (as used very successfully in swimming pools). These are ideal at trapping and removing even the finest of particles without clogging or blocking too frequently. A sand pressure filter requires a substantial surface-mounted pump and can be used successfully as a separate dedicated system separate from the main pump and filter system. They can be added just as a UV can be added to an existing pond and filter system and because it does not operate by biological means, it can be used intermittently as and when water clarity dictates.

Kill blanketweed and string algae.