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How should I clean my pond? When should I clean my pond?

11 years ago

Some ponds are never cleaned and the ponds and its occupants survive very well. However, a large number of ponds are created with high fish densities or are built in locations were the pond receives a great deal of debris over the year. Even if you start out with just a few fish initially, in a healthy pond they will breed to the point that the number of fish will push the environmental limits of your pond and biofilter. The debris may be the result of leaves blowing into the pond, the die-back of vegetative pond plants as well as fish wastes. It is these latter types of conditions that will necessitate you cleaning the pond eventually. The two most likely time points for cleaning are in the fall, to reduce the amount of accumulated muck on the bottom of the pond as you head into winter, or in the spring to remove material accumulated over the winter from leaves blowing into the pond, accumulated fish waste or catkins and similar materials shed by trees as they leaf out. Cleaning in the fall reduces wastes in the bottom of the pond which may turn anaerobic if sufficient oxygen is not available, creating a breeding ground for harmful bacteria, or which may decompose, releasing ammonia and other dangerous chemicals that can be trapped under the ice. The build-up of these pollutants can lead to fish kills over the winter months. While keeping a hole in the ice over winter will help alleviate the accumulation of gases, cleaning the pond before winter sets in will reduce the overall potential for problems. Cleaning the pond in the spring may help reduce diseases and parasites that often occur as the pond and its biology warms up for the summer, as well as reduce the overall availability of nutrients that stimulate algae growth. The following are a few approaches that have been successfully used to clean the pond.

1. If the pond has a bottom drain periodic changes of water (typically 10% per week) have been used to evacuate the accumulated debris from the bottom of the pond. This simple approach minimizes the amount of material that is removed at any one time as well as adds water to the pond on a periodic basis. Care must be taken when adding water to be sure that you have minimized the addition of chlorine and chloramines typically present in many municipal water supplies. This can be done either by pre-treating the water with dechlorination agents or by using a whole-house water filter with an activated carbon cartridge.

2. Using a net such as used in swimming pools is helpful for cleaning out large materials that have settled to the bottom of the pond. However, if there is a very large amount of debris in the pond you should be careful to either remove the fish or use supplemental aeration to avoid creating significant oxygen deprivation due to stirring up anaerobic or large amounts of oxygen-consuming muck. If you notice a rotten egg smell this indicates the presence of hydrogen sulfide. You should immediately stop stirring up the bottom and get the fish out of the water as soon as possible before continuing with the cleaning.

3. You can use a variety of devices for vacuuming the bottom of the pond. Some of these use a garden hose to create a suction through a venturi device. The potential problem with these devices is that the pond may fill up with too much water during a prolonged vacuuming and you may have a potential problem of adding chlorine and chloramines to your pond if you do not pretreat the water. Wet/dry shop vacs, specially those with an attachment for a garden hose to provide a continuous drain, have also been used. These devices may drain a large amount of water from the pond in a short time and therefore it is necessary to either replace the water or use the garden hose to add the water back into the pond through the biofilter. Care must be exercised in reintroducing water taken from the bottom of the pond in that it may be depleted of oxygen as well as have very high suspended sediment levels that may create problems for the fish. A third approach is to use a pump capable of handling a moderate level of solids (such as a sump pump) to pull water from the bottom of the pond and pass it through a device to strain out the majority of the solids and then recirculate the water back into the pond. Filtering materials such as old sweaters, panty hose, etc. have all been used with some success in this approach.
In any of these approaches, if using an electrically powered device running on house voltage make sure that you have it plugged into a GFI protected circuit for your own safety.

Ronaye, Steve and David


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