At this time of year we are often asked about how to stop a pond freezing over in the winter months when the weather gets colder.

The first thing to consider is that when the pond freezes over the noxious gases given off by decaying plants and pond life can build up under the surface. This can make your fish ill and they can even die as a result. To stop this from happening we need to make sure that there is a hole in the ice every day over the course of the winter. The hole doesn't need to be very big, dinner plate size is fine.

You must not break the ice, with a hammer or other tool. This can cause shock waves through the water that can make your fish ill.

The simplest low-tech way to make the hole is to boil a pan of water and then place the entire pan (not just the water) on the top of the ice and go have your breakfast. When you get back you can take out the pan and you'll have a lovely round hole in the ice. Repeat this each morning while the frost lasts and things will be fine. Don't rest your pan where it can touch your pond liner, as it might melt.

If you don't fancy that each morning the simplest solution is a pond heater. These are basically heating elements that have a float attached. The element gets warm and keeps a small area of the pond free of ice. They usually come with a decent length of cable (5 or 10 metres) so you can plug them in in the garage or shed, don't forget to use a circuit breaker as these are mains powered. This kind of pond heater ranges from 50 watts, for very small ponds through 150 up to 300 watts. It is worth considering only turning it on overnight as running one all the time can get expensive, although most winters they are only needed for a week or so. Oase have a version called the IceFree Thermo that has a sensor so it only comes on when the air temperature is freezing and so this model will save you money.

The other alternative is an air pump and polystyrene ice preventer. The ice preventer floats on the surface of the pond and air is pumped down a tuvbe that fgoes thourgh the middle. This air then bubbles back up to the top dragging some warmer water with it. This should serve to keep a patch ice free in all but the worst of weathers. The advantage is that air pumps are very cheap to run by comparison with heaters.

If you want to heat the whole pond then there are heaters available that will fit into the hose between your pump and filter. These start at 1 Kilowatt, so about the same as a 1 bar electric fire. 1 Kilowatt should increase the temperature of 1000 litres by 1 degree in 1 hour so heating a pond of any size can get very expensive. The heaters come with thermostats though so if you just want to nudge the temperature above freezing then they can be a good idea.