Garden Water Features – Water Quality

Garden Water Features – Water Quality

Water is the most important element in a garden pond, and its effective management is vital to ensure the good health of all the living organisms that depend upon it. The water in a pond is required (by fish, at least) for every aspect of life: to carry oxygen from the atmosphere to the gills, so that the fish can respire; to remove carbon dioxide; to carry away ammonia; to enable the fish to move; and to prevent them from becoming dehydrated. As you can see, the water in a pond is almost a self-contained ecosystem, only interacting with the atmosphere to exchange gasses such as oxygen and carbon dioxide. The toxic wastes that are released into the water must be broken down in the water, otherwise they will quickly reach dangerous levels and will kill the creatures living in the ecosystem.

Fortunately, there is a naturally occurring process, known as the nitrogen cycle, that will prevent the build up of toxic waste, provided everything is working correctly. However, it is a wise precaution to monitor the levels of key chemicals, especially during the summer.



There are many test kits and water quality rectifying products available, and the novice may be excused for being daunted by the prospect of testing pond water for the first time, especially if not scientifically minded. However, those fears should prove unfounded. The best test kits are easy to use and come with full instructions on how to resolve any of the problems that testing identifies. Often, the solution to a water quality problem can be achieved before it becomes serious enough to cause death or disease in the fish. This is a very real threat if a water quality problem is allowed to deteriorate. Therefore, testing and maintaining water quality should be viewed as essential preventative action.



The balance of plant growth, which should ensure water clarity from the outset, and the responsible introduction of fish generally ensure that still water will be of acceptable quality. How stable this balance remains will depend upon the size of the pool. It is much easier to keep a stable balance in a large pool than in a small body of water.

Still water becomes thermally stratified during the heat of the summer, because the sun’s warmth is absorbed near the surface and cannot penetrate the depths. Small shallow pools may stratify when the day is warm, but return to a uniform temperature at night as the surface layers cool and sink to mix with lower layers. These rapid changes can cause problems in both the supply of oxygen and the blooming of algae.

In very deep pools, the changes are seasonal rather than daily. In early spring, a clear distinction develops between the upper, warm epilimnion layer and the lower, cold hypolimnion layer. Between these layers is a transitional zone called the thermocline. These all have an influence on the behaviour of aquatic life, as the layers do not mix.

The lower layer receives no oxygen, but does benefit from organic debris scattered into it from the upper layer. Conversely, the topmost layer receives none of the results of decay and, by the end of the summer season, will be short of nutrients. This, in turn, can affect plants like floating aquatics, which only occupy that zone. This is why, in larger bodies of water, floating plants sometimes appear to go into decline towards the end of the summer. These distinct zones continue until the turbulence created by autumn gales mixes them and, of course, they cool down naturally.



The importance of acidity and alkalinity in a conventional garden pool cannot be overestimated. A test kit is an essential tool, which should be used at least once a month during the summer.

The acidity or alkalinity of the water is indicated by its pH value. Pure water has a pH of 7.0, which is neutral, being neither acid nor alkaline. In a pond, many chemicals dissolve into the water, and all of these chemicals will have an influence on the pH. A pH value between 0.0 and 7.0 indicates acid conditions, while a pH between 7.0 and 14.0 is alkaline.

Pond fish will thrive best in a pH of 7-8, although anywhere between 6.0 and 8.5 is acceptable. If the pH falls outside this range, pH adjusters should be used to achieve a suitable level. If the pH is consistently high, you should investigate and find the cause. In many cases, it can be traced to untreated concrete on the pond surround, a statue in the pond, or even an old house brick used to support a planting basket.

Algae also has an influence on pH: if the pond is heavily infested with algae, the pH value may change by as much as 3.0 between morning and evening. This is because the algae use carbon dioxide and remove carbonic acid from the water during the day, thus raising the pH. After dark, the algae stop photosynthesizing and produce carbonic acid, thus lowering the pH.

water soldier (Stratiotes aloides)

Some natural indicators of acidity and alkalinity can also be observed. For example, if the water soldier (Stratiotes aloides) floats freely with its spiky leaves projecting well above the surface of the water, the conditions are alkaline; if it does not float properly and becomes suspended in the water, acid conditions prevail. Likewise, if snails have shiny unblemished shells, the water is alkaline; if they become pitted or thin, it is acid.


To ensure a stable pH, the filtration must be good, and neither organic nor inorganic elements must be allowed to build up.



Aside from the decorative benefits of moving water, there is a practical bonus in that it not only provides the ability to filter water, but also assists in the exchange of gases, especially oxygen and carbon dioxide. Its only disadvantage is the constraint it places upon the cultivation of waterlilies and other deep-water aquatics in the smaller pool. The circulation of water is invaluable in the smaller pool, however, for the lower layers of water are brought to the surface and gaseous exchange is enhanced. The surface water of a still pond has a limited ability to create such an exchange, and problems can result at night when heavily planted pools may become almost depleted of oxygen.

Care must be taken with the movement of water, for in some circumstances (though not generally in a garden pool), such as in deep water where deoxygenation has taken place during the summer and all but the anaerobic bacteria have disappeared, dragging this into the upper layer of water will be counter-productive. Instead of retaining high-quality water within the epilimnion layer, it becomes contaminated by the toxic by-products of anaerobic decomposition, resulting in very unpleasant pollution.

If you are contemplating keeping koi carp, moving water will be essential, but the whole set-up will be very different from that found in the garden pool. While the koi will greatly enjoy swimming and leaping about in swirling water; the water movement will be an essential part of the entire filtering process and the maintenance of high-quality water.



Chlorine is added to domestic water supplies to reduce bacteria levels and make the water suitable for human consumption. It is best removed either by filtering the water through a carbon filter or, more commonly, by using a proprietary dechlorinator. Increasingly, water authorities are using chloramine, as it is more stable than chlorine. This will be removed by traditional dechlorinator products, but in the process ammonia will be released into the water. Therefore, it is advisable to treat the water with a bio-start product soon after using the dechlorinator to breakdown the ammonia.


18. March 2011 by admin
Categories: Gardening Ideas, Water Gardening/Water Features | Tags: , | Comments Off on Garden Water Features – Water Quality


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