As temperatures start to fall, fish in garden pools are less active, aquatic plants finish flowering and it is easy to get the impression ponds can be forgotten until spring. In fact, it is one of the most important times to be active. Falling leaves, if left to decompose in the pond, can pollute the water with dissolved waste substances that are harmful to fish. The process of decomposition can also lead to a drop in oxygen levels, and the extra organic matter will provide a breeding ground for potentially harmful bacteria. It is important to either remove leaves from the pond promptly or prevent them from falling in by covering the pond with a net for a few weeks. Autumn is the best time of the year to give the pond a good clean, as the increased pace of life down there during summer will almost certainly have resulted in the accumulation of sediment. It is far less stressful to clean the pond now, while the fish are still reasonably active and strong after their summer feed-up, than to do it in the spring when they are awakening from semi-hibernation. The best way to clean the pond is with a pond vacuum, of which the electric variety is the most efficient. These can often be hired for the day from water gardening centres and make short work of removing accumulated debris and sediment. At the same time you can also remove and tidy up any pond plants that have become overgrown during the summer. The filter and pump should be given a good clean, taking care to only wash the biological filter media in a bucket of pond water, so as to preserve its population of filter bacteria. After the clean out, the pond should be topped up using tap water conditioned with Tetra WaterSafe to remove hazardous chemicals such as chlorine. In most cases - unless the pond is emptied - the fish will not need to be removed during this process. Although fish need much less food during winter, they can still benefit from a suitable source of nutrition to keep them healthy through to the spring. Fish that have been fed sparingly with a winter feed are generally more resistant to health problems during the first warm spells of the new year. Continue to give summer food, reducing the amount as the fish take more than a few minutes to eat it. When the water temperature drops to 10C (50F), generally towards the end of October, switch to wheatgerm sticks which are more easily digested at low temperatures. Give food only when the fish rise for it and remove any that is uneaten. Once autumn turns to winter and water temperatures drop to around 5C (41F), stop feeding fish and, if possible, move the pump up on to a marginal shelf or raise it on an upturned bucket. Ideally, waterfalls should be diverted and the water from the filter returned via a submerged pipe. This reduces water turbulence and helps to maintain a warm layer of water at the base of the pond. Unless there is a danger of the entire system freezing, the pumping and filter system should be left on throughout the winter. This helps to maintain a reduced population of filter bacteria, which will quickly re-establish once temperatures warm. One of the main causes for spring health problems is the loss of bacteria from filters that have been turned off over the winter. If you are not able to move the pump and divert the waterfall, leave the system running but turn the power off when frost threatens, to avoid circulating the coldest water to the bottom of the pond where fish and other creatures seek a relatively warm refuge. If you have an ultra-violet light, either built in to the filter or independent, this can be switched off, as the algae that cause green water tend to die off during the colder months. Power to the filter is needed only for the UV light. Filtration takes place naturally as the pump forces water through the filter. Ice can cause problems for ponds in the winter. It traps harmful waste gases that build up and pollute the water, harming both fish and hibernating frogs and other amphibians, and also stops oxygen being absorbed into the water. In addition, a lack of water poses a real problem for birds in winter, as they need water to drink and clean their feathers. Small birds need to drink twice a day in the winter and dirty feathers do not insulate or waterproof properly. There are various ways of trying to prevent ice from sealing ponds - floating a ball, etc - but the method I have found to be easiest and most effective is to invest in a Tetra Winter Island heater. This is effectively a floating bird bath, containing a small area of water that it keeps warm with a low wattage heating element. It comes with 7m of cable and is plugged into an outdoor electricity socket. Gases can pass in and out of the pond through this pool of water, and it is designed to allow birds to bathe and drink in it. However, don't try to break ice. Blows send shock waves through the water that are very stressful to fish. | 
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