Garden Pool Upkeep
I am often asked about the amount of upkeep or maintenance a pond requires, but the answer depends on a number of factors that vary from pond to pond. One pond may need very little care, whereas another, due to its size, the plants and fishes that it has been stocked with, and the type of water and construction used, will need a steady flow of attention throughout the year.
Let us take as an example a pond that has a complicated shape with narrow inlets, shallow shelving water and overhanging trees. The shape will at once encourage parts of the water to stagnate; the shallows will breed algae; and leaves will drop from the trees into the water, causing putrefaction. The insect population will increase in certain groups,will run riot, and diseases affecting plants and fishes will increase too.
If we take an alternative pond, with a simple shape so that the water can circulate freely, placed in the open with a balance of plants and livestock, then the amount of attention it needs will be minimal – only an occasional thinning of plants if they become too rampant, and checking the fishes for health and vigour.
If you live in a wooded area, autumn leaves can be a problem, falling into the water and sinking to the bottom where they decompose and give off noxious gases. To prevent this occurring, spread a fine net over the water surface to catch the leaves; where there is a large stretch of water, lay the net in sections across the pond so that they can be lifted off piecemeal to remove the leaves.
Weather, too, can cause some additional upkeep. Frost may seal off the water surface, preventing oxygen from reaching the unfrozen water and stopping toxic gases escaping; this is not critical over a short period, as the cold will have made the fishes slow down and they need less oxygen, but there is a danger of ice expanding and cracking or splitting the pond container, whether it is a precast shell, a liner or a concrete pond.
If the pond has been designed with sloping sides the ice will be forced upwards without damaging the structure. A pond heater can be floated in the pond; when switched on, this will keep a small area unfrozen around it, allowing both oxygen and fishes to reach the surface, and when the ice expands the pond container will not be damaged. A cheaper method is to drop a large floating ball into the water, and remove it when the water freezes, to leave a hole in the ice for air to reach the unfrozen water; replace it at night when the temperature drops. The expanding ice will lift the ball, and thus also lower the risk of pond damage by relieving pressure.
Never break the ice with a heavy blow, because the shock waves will pass through the water and can stun or kill the fishes. It is better to use a hot object, a metal bar or a can filled with boiling water, to melt the ice, which can then be lifted off and broken up away from the pond. Sometimes if the weather continues freezing it pays to drain off some water under the ice, leaving 2.5cm (1 in) or so of air between ice and water; this will act as a form of insulation, and still keep some oxygen in touch with the water.
In very hot weather there is a danger that a small pond will get too warm and the oxygen level become dangerously low, causing the death of the fishes. To prevent this, increase the level of oxygen by pumping the water through a fountain; the drops of water will be recharged with oxygen before returning to the pond.
Additional oxygenating plants will absorb the carbon dioxide given out by the fishes and return oxygen to the water, and help the pond balance; they will also prevent sunlight from reaching some areas of water and thus stop the growth and spread of algae, which increase in hot weather.
Another thing to watch for in hot weather is the rapid evaporation of water. This can lower the surface quite dramatically and expose the liner, if one has been used; sunlight on exposed plastic can speed up deterioration, making the liner brittle and hard so that it cracks, allowing the water to seep away.
When the pond level drops, top it up using a hose. Because the water needs time to adjust to the surrounding temperature, it is better to top up with a little extra water several times, rather than to allow the surface to drop a long way and then have to pour in large quantities of raw tap water. A little tap water will dilute with the pond water, and the chlorine and other minerals will have time to disperse before the next topping up takes place; this will cause less distress to the livestock.
Occasionally the pond will have a sudden influx of algae, usually afterhave been thinned out and fed, especially if this coincides with a period of uninterrupted sunshine. This sometimes happens when you wish to show off the pond to friends, and an immediate remedy is called for. The answer is to use a dose of algaecide, which can be obtained from most aquatic centres and specialist shops.
If the water becomes too acid, due to rain or seepage, it is important to redress the balance. This can be done by placing a lump of limestone or chalk in the water until it becomes neutral again. Use a water testing kit to check the pH value finally.