Technical Index
Aquatics Home
Pond liners
UVC Clarifiers
Fish Food
Test Kits
Pond Calculators


The various options available to the pond keeper as the winter approaches, fall into two main categories:

Continuation of filtration.

Removal of filtration.

The decision is primarily determined by comparing the benefits of continuing filtration, which will help to sustain some degree of biological colony and reduce the risk of the pond freezing over, compared to the running cost and danger of low oxygen due to freezing.

From a biological point of view, the continuation of filtration in a heated pond is essential. In an unheated pond, continuation will improve the speed of biological maturation at the beginning of the following season and give some protection in the event of winter warm spells.

Winter Running for Unheated Ponds

For winter running of unheated ponds, here are a few tips to ensure that your fish have a happy winter:

Gravity Fed System

If the inlet system is a Multi Level Inlet, the bottom inlet should be closed off so water is only drawn from the top of the pond. If a bottom drain is being used, a reduction in the flow rate can help to minimise the water temperature dropping.

Pump Fed System

Position the pump in the top third of the pond and closer to the filter release point. This will reduce the circulation and allow the bottom of the pond to remain warmer.

General Points

Remember that returning water helps to prevent the pond surface from freezing, which help the oxygenation of the water. Therefore, the returning water pipe(s) should release above the surface of the pond (if the surface of the pond is moving, it will freeze at a lower temperature).

If you have a waterfall, fountain or venturi, they should be bypassed or switched off, as the exposure of the water to the cold air, causes a chilling effect which can be harmful to the fish.

You should switch off, drain and remove the Ultra Violet Clarifier if there is any risk of freezing. If the water is allowed to freeze inside the UVC, the expansion of the ice will cause the quartz tube to crack.

By leaving the filter system running in the winter you will find that your filter will mature quicker in the spring ready for the new season.

If severe weather is predicted, switch off and drain the entire system (see Winter shut down section for details).

Winter Running for Fully Heated Ponds (not a floating pool heater)

As the purpose of heating a pond during the winter is to maintain continuous summer conditions, we advise that the filtration system be run as in the summer months. However, the following are a couple of points to ensure that all goes well:

If the heating system of the pond should fail, the water temperature could fall rapidly, which would be harmful to both the fish and the biological colony. We therefore recommend that a backup heating system is available.

If the filtration system is installed above ground, try to insulate the outside of the filter to avoid heat loss.

If there is any risk of the system freezing, you should switch off, drain and remove the Ultra Violet Clarifier. If the water is allowed to freeze inside the UVC, the expansion of the ice will cause the quartz tube to crack.

Avoid using waterfalls, fountains and venturis as these will chill the pond. This will increase the costs of heating and may also lead to areas of the pond being at different temperatures.

Winter Shut Down

If you wish to shut down the filter systems during the winter months, we would recommend the following:

The system should be left to run for at least 2 weeks after feeding has stopped and restarted approximately 3 weeks before feeding commences in the spring.

Never feed your fish whilst the filter is out of operation.

Once removed, the filter and UVC should be thoroughly cleaned with tap water and stored indoors.

If removed, the pump should be cleaned and stored indoors. If the pump is a Prima, it should be kept in a bucket of clean water to prevent the seals drying out and cracking.

If the entire system is removed, we advise that a small pump is used to disturb the pond surface or a floating pool heater is installed. This is to try and prevent the pond from freezing over to allow oxygenation of the water.

Winter Maintenance

Whether the filtration system is removed or run during the winter, it is a good idea to do a little cleaning before the weather becomes too bad. We would recommend the following:

The pond plants will start to die off as the weather becomes colder, we would advise that the plants be trimmed back to ensure that the dying plants do not pollute the water.

During the season, the base of the pond may have developed a layer of silt and sediment. We recommend that this should be removed with the use of a Cypri-Vac or similar device.

Please note that the above recommendations are based on our experiences over the years and not intended to be a definitive procedure or guide. Particular care should be taken with small ponds, if moving water is used to prevent freezing over, the chilling effect is very hard to avoid. In this situation it may be safer to shut down the filtration system and use an alternative method of preventing freezing. If, however, you are in any doubt as to what action to take during the winter, consult your local specialist.