Cloudy pond water – I can’t see my fish!

I installed a new 2000 gallon pond in March of this year, constructed using a liner and incorporating an external multi-chambered filter. I have been adding koi to it since Easter and have noticed that the pond’s clarity has deteriorated from its initial crystal clear state so that I can no longer see the pond bottom. I have tested my pond water and the pH is 8.0 and the nitrate 30ppm which I believe is acceptable. I have also noticed that my koi appear to have been eating less recently (although that could be down to the cooler weather). Why has my water clarity deteriorated and what can I do to return it to its former glory?

A: Murky water is not necessarily an indicator of poor water quality, in the same way as crystal clear water does not always represent perfect water quality. Let’s not forget that we want our ponds to be clear for our benefit – so that we can view our koi easily. If you were to ask your koi what water conditions they would prefer, then they would vote for murky, cloudy water every time – as found in the mud ponds of Niigata.

I suggest that your priority should be to carry out a full water quality test as this will give you a greater understanding as to how good your water quality really is. Either buy ammonia and nitrite test kits or ask if your dealer will test a sample of your pond water for you. I personally would prefer to buy the test kits as this will allow you to monitor your pond at regular intervals. Your pH and nitrate readings are acceptable for koi (even though the nitrate readings should be as low as possible) and when tested, your ammonia and nitrite readings should be zero.

It is a little worrying to read how immature your pond is and suspect that the ammonia and nitrite readings will prove positive – having a negative impact on your fishes’ appetites (which you suspect) and possibly attributing to the cloudiness of your water. I can’t comment further until you report back with your ammonia and nitrite readings.

At this stage, it may be more helpful to look at some of the possible causes of cloudy water in your new pond to see if any of them sound plausible for your situation. But the priority is still for you to test your water more comprehensively.

Most instances of cloudy water will still allow us to see the pond bottom, where the water has merely lost its sharp focus, but your case sounds more extreme than this. 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 when displaying your koi. Assuming that the water turnover rates and the removal of solids from your pond are adequate, there are a number of likely causes of cloudy water that you could be looking at.

1. New and Unbalanced Pond.

As a pond takes several seasons to become fully mature, yours is still very immature. This means that the numbers and variety of micro-organisms that are found in your pond are far smaller than they would be in a fully mature and balanced aquatic ecosystem. Consequently, a new and unbalanced pond is more likely to suffer from a clarity problem. New ponds are often overfed or overstocked in relation to the biological action of the immature filter, leading to an inevitable water quality problem. An ammonia or 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 an ammonia or nitrite problem, the cloudiness disappears as well. That’s why you should test for ammonia and nitrite as a matter of urgency.

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 your filter media, they produce a sticky, slimy substance, which will 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. Algae.

Algae could be the cause of your cloudiness. Excessive algae growth suspended in the water can make the water resemble pea soup and by your description, your pond could be well on the way. You do not mention whether you have a UVc installed with your filter system as this is a guaranteed method of solving a green water problem. If you do have a UVc and a milky hue returns to your 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). Probably not applicable in your case unless you bought it second-hand.

b. Excessively hot and sunny weather means that the UV is not keeping pace with the increased production rates of algae. This deterioration in clarity should improve with milder weather.

c. The UVc you have installed is not sufficient to clear the volume of your pond. Check that the wattage of your UV is rated at at least 2000 gallons.

3. Food could also be causing the water to cloud or change colour. Water can become cloudy having changed to different foods or brands and if this is the case, it is quite possible that the change has been the cause of your water’s turbidity.

Food-related problems may arise from poorly bound ingredients breaking up once the food comes into contact with 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. Ask your koi dealer what food they would recommend that you use.

What are the other possible solutions to your problem?

If your water chemistry is satisfactory, and the algae is not the cause then the solution to improving your water clarity is to enhance your filtration and particularly mechanical filtration.

The most common, limiting factor of a filter is its ability to remove the finer suspended 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 your filter is unable to remove even the smallest of solids then you will never be able to achieve crystal clear water.

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 your 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 the clarity of your pond water dictates. A more recent entrant to the mechanical filtration market – ‘The Answer’ uses an ultra-fine micron mesh screen that is permanently backwashed ensuring that even the finest of particles do not pass through your first chamber. Units for smaller ponds such as yours are now available, and if this does not reduce your water clarity problem please get back in touch.

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