Jimmy Hepburn from Devon based Aquavision looks at cleaning out ponds, one of the most frequent requests he gets asked running his pond business
There are four key questions to ask when considering cleaning out a pond.
Cleaning a pond can be a messy job which is not for the faint hearted! Over time, ponds accumulate silt from dead leaves, fish waste or last season’s water plant growth. The breakdown of the silt slows down due to lack of oxygen in the silt. When the accumulation of silt exceeds 15cm in depth the health of the fish and the plants can suffer.
2. How often does a pond need to be cleaned out?
This can depend on:
• Size - smaller ponds (less than 9m2) will normally need to be cleaned out more frequently than larger ponds.
• Trees – if there are trees near by, any leaves which fall into the pond will add to the silt load.
• Stream – if a stream passes through a pond, during times of spate, then the sediment carried in the stream is likely to settle in the pond adding to the silt loading.
• Water plants – excess growth of water plants (both marginal and submerged) which ‘choke’ the pond will necessitate a clean out.
• Fish – high stocking rates can lead to significant accumulations of fish waste which ultimately can be toxic.
As a rule of thumb a pond of nine to 16 square metres should require a complete clean out every five to ten years years. For larger ponds it may be longer.
The times to avoid are either when it is very cold or hot – as this can cause undue stress to fish and plants. Late spring or early autumn are ideal. If you have any amphibians in the pond which have bred then it is probably better to clean the pond mid to late autumn.
Cleaning out a pond can be a messy business, so some preparation is important. I suggest the following:
• Set up storage tanks for fish and pond wildlife (with a cover) as well as to hold some of pond water to ‘seed’ the new pond.
• You will need a pump to empty the pond (if there is a pump already in the pond this can be used).
• A hand net and bucket to catch the fish.
• A brush, straight edged bucket and dustpan to collect silt.
• A stiff brush or pressure washer to clean the pond liner after it is empty.
• A tarpaulin to be laid beside the pond to minimise mess.
When you have all the preparations in place start to pump out the water (remember to fill the holding tanks with clean pond water first). When about two thirds of the water has been pumped out you will find it easier to remove the plants and catch the fish.
Depending on the shape of your pond and the pump you are using, you will then have to start removing the silt from the bottom of the pond. A brush and dustpan can be useful and remember to be careful not to damage the pond liner.
With an empty pond you can carefully scrub the bottom and sides and rinse out with clean water. Examine the condition of the pond lining. This is the one opportunity to change things in the pond (or carry out repairs).
Finally it is time to start filling the pond again. If you have a store of rain water add that to the pond first followed by some of the pond water and silt you set aside earlier. Top up with mains water – but remember a hose running at about 15 litres per minute will take around five hours to fill a 5,000 litre pond.
As mains water contains chlorine, a delay of stocking the pond by 24 hours is needed to vent the chlorine. Alternatively, by adding a chlorine neutraliser such as ‘Fresh Start’ fish can be returned immediately.
Repot any lilies and marginals with new baskets (if necessary) using aquatic compost along with a top dressing of gravel. Lastly return the fish ensuring that the water temperature you are adding the fish is similar.
Now you can sit back and relax for the next five to ten years.
Jimmy and Penny Hepburn run Aquavision, a business specialising in carp, aquaponics, training courses and professional pond services.