Cold Water Ponds and Fish: Care and Maintenance

In summer, water-loss by evaporation can cause problems. In a pool of small capacity the level is watched constantly and the pool kept topped-up. Tap water should preferably be ‘aged’ to allow chlorine to escape before adding it to the pool. A day or two should suffice. If the level is allowed to drop, the liner can become exposed which, besides being unsightly, it may become brittle by constant exposure to hot sun followed by cooling at night.

If the water becomes too warm it reduces the amount of oxygen that it can hold and fish can sometimes be seen gulping air at the water surface. A fountain overcomes this problem as it oxygenates the water and also cools it by evaporation. Remember that loss by evaporation may be higher if a fountain is in constant use, so more regular topping-up may be required. In emergency a garden hose played on the surface will re-oxygenate the water and increase the water level, but the fountain is the only answer to oxygen starvation in the long run. A large pool with a high capacity is also less prone to these problems, and if your area is blessed with long, hot days you should not consider the smaller pools.

As leaves die off they should be removed to avoid the build-up of harmful gases in the water due to their decomposition. Information on individual plant care will be found in the identification guide section. Large aquatic plants may be divided in Spring and replanted in fresh planting medium.

`Green Water’ is sometimes a problem. This green colour is caused by millions of unicellular green algae, and whilst small amounts provide welcome fish food, an abundance is unsightly and makes your pool more difficult to maintain. Excessive algae growth is usually caused by too much sun, and shading all or part of the pool may help to control it. Water lilies, with their broad leaves may offer some protection. Algae can be killed off by using one of the many products supplied by aquatic dealers and some of these offer protection against other troubles such as white-spot disease, fungus and blanket weed – a type of filamentous algae resembling thin green threads which adhere to the pool sides. The instructions should be carefully followed to avoid harm to your fish. It is wise to flush the pond through by trickling a hose in at one end and syphoning out at the other. This gradually changes the water and enables the remaining algae to be killed without pollution of the pond bottom. A crystal clean pond does not look right, and you may remove essential food by overzealous cleansing. So any pond cleaning should be restricted to keeping the water clear. Once a balanced environment is set up, very little attention should be required to keep it that way.

In winter the only major problem is that caused by the pond surface freezing over, which seals in toxic gases and prevents usual oxygenation taking place. To avoid the surface freezing, a rubber ring left floating on the surface will help, but a careful watch should be kept and if the surface freezes the ice should be broken and removed as soon as possible. Heaters are now available to prevent surface freezing and should be used whenever frost is possible. There is a danger that these might be left switched off when needed, so they are far from infallible.

Cold Water Pond Fish Care

Daphnia or Waterfleas are an important source of food for infant fish and they can be useful to clear pools of algae, which is consumed avidly. When used to clear ponds of algae, all fish should be removed until the daphnia have done their work. The fish can then be replaced when the fattened daphnia will quickly be gobbled up. Daphnia appear naturally in water above 10 degrees C but eggs can be bought from aquatic stores and introduced into the pool immediately, or reared and the fry put in.

The amount of oxygen required by a fish varies according to its size, large fish take more oxygen than small fish and require pools with a larger surface area. Remember that fish grow and a pond which supports 20 small fish may be too small for the same number when mature. If fish are seen sucking air at the surface, oxygen deficiency should be suspected.

Excessive feeding is a common cause of water pollution. Fish should be fed sparingly or allowed to feed from a self-help feeder.

Pond fish are generally non-aggressive and will readily mix, providing they are not over-crowded. If cover is provided by plenty of plant life, this is beneficial to breeding and prevents the fry from being eaten.

Providing attention is paid to pool cleanliness and over-feeding is avoided, you should have little problem in maintaining your pond fish in good health. There are some diseases and ailments which can prove troublesome.

A special tank with a heater and thermostat can be set up for ‘hospital’ treatment of sick fish. Speed is essential if disease is to be cured and, more important, if its spread is to be halted. It is a good idea to study your fish carefully each day, and any suspect fish can be removed for observation at the earliest sign of trouble. When placed in the tank, the temperature can be gradually increased to 23°C – sudden changes should be avoided. If you are late in spotting disease and the whole pond becomes infected, change 50% of the water immediately and add some aquarium salt, about one tablespoon to a gallon of water.

Diseases Affecting Cold Water Pond Fish


Fungus or Saprolegnia, normally attacks damaged areas of tissue, or can be brought on by sudden changes of temperature, and unless eradicated will prove fatal. A strong salt solution -three tablespoons to the gallon can be used in the hospital tank, and the solution changed frequently – twice a day if possible. After a few days, the fungus should be destroyed.


This can be readily identified by the tiny white blisters that appear on the sides of the body. It is highly contagious and signs should be watched for on the other pond inmates. Methylene blue is the usual chemical used to disinfect the hospital tank, and 3 drops of 5% solution per gallon of water should be used. A strong salt solution is another alternative and this together with a temperature of 23-25°C is usually effective.


A fine thread protruding from a raised pimple is a sure sign of anchor worm infestation. When touched, the thread can be seen to withdraw. Turpentine applied carefully with a fine camel-hair brush can be relied upon to despatch these pests quickly.

11. July 2011 by admin
Categories: Garden Ponds, Pond Fish | Tags: , | Comments Off on Cold Water Ponds and Fish: Care and Maintenance


Get the Facebook Likebox Slider Pro for WordPress