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MAINTAINING WATER QUALITY IN THE POOL

The balanced planting of a pool should produce good water quality, but such quality from the point of view of the plants and fish is not necessarily the same as clarity. Indeed, water with a slight green algal bloom or a warm amber colour is probably as pleasant an environment for the fish and snails as the harsh crystal clear clarity sometimes achieved by filtration.

The importance of acidity and alkalinity with regard to a garden pool can be over-stressed. A test kit is a useful adjunct to the chemical cupboard, but it usually proves to be a tool which confirms what you already appreciated, and that the pH is between 6.0 and 8.0, which is perfectly acceptable for almost everything, both fish and plants. Excesses either way are rare.

There are also natural indicators of acidity or alkalinity. If the water solider, Stratiotes aloides, floats freely with its spiky leaves pointing well above the surface of the water, then the conditions are alkaline, if you fail to get it to float properly and it becomes suspended in the water, then the conditions are acid. Likewise, if snails have shiny unblemished shells the water is alkaline, if they become pitted or thin, then it is acid.

Acidity and alkalinity only cause difficulties when they are extreme, and usually there is evidence of problems with the growth of plants and development of fish which although not necessarily directly and obviously attributable to the state of the water, would cause even the most inexperienced water gardener to consider testing the water.

If you read the catalogue of an aquatics specialist or visit the water garden department of a garden centre, you could be forgiven for thinking that the control of water quality was the most important element in water garden management. There are cures and antidotes for every water condition and products that also improve the quality of the water. All are perfectly legitimate and practical, but only when there is a problem, which if the pool is planted and stocked responsibly is likely to be very rarely.

The need for many of these medications and detoxicants is only likely to arise when there is an over-population of fish, or if koi carp are kept in large numbers without plants, such as is the case with the enthusiast.

Chlorine is probably the chemical that will present the most concern, although it rarely produces serious consequences in a garden pool. It is true that a pool which has been recently filled with tap water may be laden with chlorine, but during the warm summer weather it evaporates quite quickly. If you are still concerned about its presence, then there are products which will neutralise it. The main problem with chlorine is the irritation which it causes fish, in severe cases causing extreme discomfort and reddening around the gills.

The balance of plant growth, which should ensure water clarity, together with the responsible introduction of fish generally ensures that still water is of acceptable quality. How stable this balance is depends upon the size of the pool. In a large pool it is much easier to keep a stable balance than it is in a small body of water, despite the fact that both are effectively closed ecological systems.

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 and sunny, but become uniform again at night as the surface layers cool and sink to mix in with the lower layers. These rapid changes can cause problems with both the supply of oxygen and the blooming of algae.

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

The lower layer receives no oxygen, but does get organic debris scattered down into it from the upper layer. Conversely this topmost layer receives none of the results of decay and by the end of the summer season is short of nutrients, which 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 like this until the turbulence created by autumn gales and rain mixes them up.

Aside of the decorative value of moving water there are practical ones in ensuring a consistency of water quality. Not just by providing the ability to filter water, but by assisting in the exchange of gases, especially oxygen and carbon dioxide. Its only disadvantage is the constraints which it places upon the growing of waterlilies and other deep water aquatics in the smaller pool. The circulation of water is invaluable in the smaller pool, for the lower layers of water are brought to the surface and gaseous exchange is enhanced.




 

 

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