Your new house has a pond. What to do next!

Many life-changing experiences are unplanned, occurring by accident rather than by design. Consider the time that purring ball of fluff turned up at your door all those years ago and has been the most important guest in your house ever since, or the marriage proposal out of the blue, followed closely by news of a new arrival in approximately 9 months time.

Lots of peoples’ lives have been immeasurably enriched by such unplanned events, often reflecting ‘how much emptier our lives would have been today if…..had not have happened’. There is certainly a lot of evidence to indicate that this has certainly been the experience of many pond and koi keepers who, when moving house, have had a pond fall into their laps. Little did they realise that by buying the house with ‘well proportioned gardens front and rear which boast a mature ornamental pond’ (as described in the estate agent’s details) that they would discover another side to their psyche – their fish loving side.

Numerous family meetings may follow….’do we fill it in, do we want a pond or would our children prefer the water replaced by 2 tons of sand? Will it be appreciated by our children and will they be safe in the garden with a pond?’

‘If we do wish to keep it, do we rejuvenate it, or completely upgrade it? Where do we find out what our options are and what do we do if we discover there are over 20 fish hiding in there? Will we be able to keep them alive?’

Your mind may be buzzing with these and many more questions and every option should be considered.

Fill it in?

Filling the pond in is an option but may well prove to be a mammoth task possibly taking many hours of hard labour. This also assumes that when the pond was originally excavated that the soil was stockpiled next to the pond to form a raised rockery. If the spoil from the original dig is not there then where will you get the soil to fill in the hole? How big are the pieces of stone on the rockery and where can they be moved to?

Once a pond has been filled in, hundreds of pounds of investment and value will have been lost, taking many hundreds of pounds to recover the pond should you later have second thoughts.

Why keep the pond?

A pond will form the focal point of a garden offering many practical and aesthetic benefits to your garden. A living, moving landscape whose character will evolve to reflect the seasons. Attracting wildlife such as many varieties of interesting insects such as dragon flies, damsel flies and pond skaters as well as frogs, toads and even newts.

Inheriting a pond should not limit the scope to your ideas, but should act as a good basis from which to plan, be it a natural pond, a garden fish pond or a specialist koi pond, each with their own appeal.

Of course, when considering the benefits of a pond, we must be realistic and also recognise the costs. Budgets are likely to be at their tightest when moving house, with a pond that may need some money spending on it appearing on the list well below any new carpets and a fitted kitchen. If this is the case, and the pond is in need of renovation with no fish apparently in residence, it may be worthwhile putting your pond into ‘dry dock’ while you formulate your plans for the pond when budget allows. At least by cleaning out the pond you should gain a greater appreciation of the size of the your pond and the scale of your task.

This will also set your mind thinking about the options, gleaning ideas from TV, neighbours, aquatic outlets, books and magazines. Is it to be a wildlife pond, a fish pond or a koi pond? Your decision will determine how much work would be required and be reflected in your budget. The choice is yours.

The First steps. A Pond Audit.

Carrying out a pond audit will help you to determine whether the pond you have inherited. You should soon discover whether it is really worth persevering with or whether it would need a complete rebuild to give you years of enjoyment without having to roll your sleeves up again in a few years time (until you choose to extend it).

Checklist for a Pond Audit.

Pond structure – Liner, preformed, or concrete.

First impressions at this early stage may not count for a lot. Inherited ponds are rarely in a presentable state often being neglected during the period the house has been up for sale.

A good clue as to the integrity of the pond’s membrane is the water level. If the water level has dropped, it maybe through a leak or evaporation (rather unlikely in November). Filling up the pond and monitoring the level for a day or so can verify this. If there is an old and stubborn tidemark at the current level then it is more likely to be leaky above this level. This is also the time when you can determine your pond’s suitability for koi. If it is at least 3′ deep then you could venture with some small koi. Ideally though it should be deeper and approximately 2000 gallons in volume.

A. Liner Pond. Things to look out for.

Is the pond liner intact? Some liners can become bleached and brittle after years of exposure to the sun. Confirm that there is still a good degree of flexibility in exposed areas of the liner, around rockwork and edging as a brittle liner will indicate that it may be coming to the end of its life.

In addition, liner ponds can often suffer from slight subsidence and movement of earth beneath the liner. Shelves may slump and begin to sag or pond edging may appear as though it might slip into the pond.

B. Preformed pond.

As long as you are able to confirm that it still holds a pond full of water, there is very little that can go wrong with a preformed pond. They prove to be very durable and UV resistant.

C. Concrete.

Concrete ponds can prove to be as reliable as preformed fibreglass ponds. However, build qualities differ and can start to flake or crack after years of frost and ice attack. If the exposed pond edging appears to be sound with no signs of flaking, then leave well alone. A good concrete pond if well looked after can last for generations.


Being new to fish, there are a number of useful guidelines to follow to make sure any inherited fish remain healthy. You may find the pond in such an overgrown and silty state that you’d find it difficult to believe that it could support fish life. Ornamental pond fish, particularly goldfish and shubunkins are very hardy and adaptable fish, living in and feeding off the organic debris in a pond and can be found thriving in the most apparently inhospitable silt. However, fish will suffer should you disturb the pond water and stir up silt and the smelly sludge from the bottom. If you are aware of there being any fish in your new pond, leave the pond well alone until you have decided to progress with your aquatic DIY project. If you have decided to drain down, then you would be stuck with finding a suitable pond for the fish. A water barrel filled with tap water is not the answer.

Pond Equipment.

The presence of existing pond equipment (pump and filter) may well help you decide whether your new pond is going to be a still, back-to-nature wildlife pond or a recirculating fish pond.

Is there a pump and filter or does the pond resemble a crime scene? Is there an obvious flattened weed-free position where the filter used to be or is it still there? Is there a cable leading down into the murky depths signifying the presence of a submersible pond pump (or has that gone too along with the shed which you also though was included in the sale?).

If a pump is present, then pull it out as gently as possible and see if it is connected to anything. You may find a flexible hose leading up to where and external filter is (or was) and even perhaps another outlet connected to a fountain or ornament. It is almost impossible by inspecting a pump’s external appearance to assess the condition of the pump. A simple service that includes the removal and strip down of the pre-filter (if it has one) and to check that the impellor spins freely should give you some clues as to its condition.

If the vendors have left you the filter as well then it is a fair bet that it will need a good clean out. Before tipping its grubby contents out on to the lawn, dismantle it piece by piece and memorise the order in which the media is set, even down to the order in which the coloured layers of foam go. Coarse at the top, fine on the bottom.

If the pond filter is not running, then you can simply give the filter a thorough clean under tap water. If however, the pond and filter are currently active, clean the filter out with pond water which is not as harsh on the bacteria as tap water.


The most effective way of assessing the variety of plants in your new pond is by draining it down, especially if there is a centre-piece lily in the deepest part.

Plants in a mature pond can often benefit from re-potting as vigorous growers such as water iris, reeds and especially water lilies can soon burst out of the strongest of planted baskets.

There is also the strong likelihood that the water will be thick with submerged oxygenating plants having spread through the water. These too should be removed, the best selected, re-bunched and re-potted in a newly filled basket.

If it is winter time, then foliage will have died back, making the task of tidying and re-potting much easier. But be careful not to discard any non-descript clumps as they may burst forth with luscious new growth in the spring. If in doubt, hold onto it until the spring.

Rockwork, paving and edging.

Tastes rarely coincide, you just need to take a look at your new house’s pink and purple bathroom suite. The same can be true for the way in which a pond is styled or finished. When considering what to do with the new pond, consider the pond and its finishing touches as a whole. If your predecessor has used broken concrete flagstones for edging and a pre-cast set of plastic waterfalls and you want to give it a more natural ‘slice of the Lake District’ effect, then flags and plastic waterfalls will have to go. A ton or so of sand stone slabs will need to be ordered for the new edging and waterfall, to be made from stepped natural stone.

Having assessed the assets and liabilities of your recent inheritance and budgeted for a renewed garden pond with crystal clear, sparkling water, what is the best method of attack?

A step-by-step guide to renovating an inherited pond.

Your inherited pond is overgrown with a variety of oversized aquatic plants, is currently running 2/3rds full and is made with a liner which you estimate is at least 10 years old. There is no pond equipment such as a pump and filter and there don’t appear to be any fish in the pond…..well you haven’t seen any.

Drain Down

Remove the water and silt by pump and bucket. There will be a lot of sludge and silt on the bottom so be prepared to scatter it on the borders – it is excellent fertiliser.

The first water that you remove will be the cleanest and should be collected in a clean barrel or sizeable container to act as an emergency pond should you find any fish hiding in the silt.

All planted baskets should be removed and dragged out on to the lawn where they can drain, giving you time to decide what to do with them. If the liner had been intact or relatively new with say a single leaking hole, it could have been easily repaired using a kit similar to one used to repair a bicycle puncture.

The old liner should be removed to allow you to repair any depressed shelving that may have settled over the years. It will also allow you to check the liner’s insulation and protection from protruding stones and roots.

Any paving stones around the pond edge will also need to be lifted to allow the removal of the old liner and the installation of the new one.

Having evaluated the suitability of the pond’s foundations, sand and underlay can be fitted to cushion the new liner. The area of liner required is calculated by measuring the greatest length and width of the pond and adding double the depth to the length and width.

Laying new liner

Having been advised by your aquatic dealer as to the advantages and disadvantages of either a PVC or butyl liner, you opt for a 25 year black PVC liner.

This is allowed to lie in the sun to become supple and laid across the hole and anchored with some rocks and filled with a hose. As it fills the liner will sag and begin to adopt the shape of your improved pond.


The root stocks of all plants, marginal and submerged, should be chopped back if necessary and re-potted in baskets. Each basket is lined and filled with aquatic soil, your newly-trimmed plant inserted and topped off with a layer of gravel. The plants are then arranged to provide coverage around the pond shelves and in the deepest part of the pond.

Pond equipment.

There are 3 essential pieces of pond equipment required to create a crystal clear pond that is suitable for fish.

A pump. A submersible pump should be installed that will pump to the desired height and will circulate the pond volume at least once every 2 hours. This will vary if you plan your pump to feed a waterfall.

A UV clarifier. The pump delivers water to the UV clarifier which sits on top of an external black box filter. The UVc requires a power supply as the light inside causes the algal cells that cause green water to clump together so they can be filtered out.

The filter consists of a black box header tank type assembly which contains an array of filter media. The filter will remove solid debris and also act as a media on which beneficial bacteria will colonise, breaking down the soluble waste produced by fish. The filter can be hidden using creative planting and some models of filter can even be buried out of sight.

Electrical Supply

This is probably the only part of your pond project that will require professional assistance.

A qualified electrician will soon install a safe, isolated power supply out to the pond. He will do it in a quarter of the time it takes you to do it and will ensure above all that the supply to your pond is safe.

Fish or wildlife pond?

If you feel that you simply want a wildlife pond that is still, tranquil and in balance with nature then no pond equipment or power supply would be required, simply a pond with an abundance of plants to keep the pond clear. For an average sized pond, this would save you approximately 400.

Cracking concrete pond?

If the pond which you encounter is of concrete construction but cracking and leaking and in need of repair, then it may well be cheaper to reline the whole pond with a PVC liner rather than patch with render, only for the structure to give way elsewhere in years to come.

To line a concrete pond, simply drain it and line it with a combination of pond underlay and sand, taking care with any sharp concrete edges.

Pond Plants

The beauty about planting a pond is that there are so many different plants to choose from that can be planted in the different zones of a pond. Take a look at Peter J May’s site … he talks a great deal of good common sense about aquatic plants in water gardens and pond


A very fast growing (sometimes too invasive) floating plant is Fairy Moss. This is very effective in a new pond at cutting down light penetration in a pond, reducing the occurrence of green water. As other plants become established, the Fairy Moss can be removed.


These marsh loving plants are planted on the pond shelves where they can be placed around the pond for different effects. Taller marginals at the back e.g. Acorus calamatus (Sweetflag) or Botumus umbellatus (Flowering Rush) with lower growing, sprawling plants in the foreground to soften and blend the edges of the pond e.g. Mimulus, Lobelia cardinalis, Water Mint and Parrott’s Feather.

Submerged oxygenating plants.

These plants are rooted at the pond bottom where they will expand to fill the water space, competing with nuisance algae for light and nutrients. These include Hornwort and Elodea crispa.

Deep water plants.

These include lilies and water hawthorn. Rooted in the depths, they will send up pads of various shapes, sizes and colours, flowering each summer. In the winter, the leaves drop off as the plant retreats to the depths for winter.

How long will it take?

A pond renovation is best carried out in the autumn and winter months when plant growth is minimal. This will allow you to prepare and fill the pond ready for spring.

The work can be divided into weekend-sized jobs.

Weekend 1. Pond audit to assess the condition and potential of the existing pond. This will include assessing and pricing up the alternatives. Empty the pond, remove the sludge and plants. Keep the plants moist in a suitable container. Does the liner or concrete need replacing? Measure up for liner. Do you need a pump and filter?

Weekend 2. Purchase the liner, underlay and sand and the necessary pond equipment. Remove old liner and repair shelves if necessary. Remove pond edging and rockwork , lay new liner and fill with water.

Weekend 3. Secure an electrical supply to the pond. Position re-potted plants. Install new pump and filter and switch on.

Weekend 4. Test water for pH and introduce first few fish.

Weekend 5-10. Continue to introduce fish and test water to determine whether the filter is keeping pace with the growing fish population.

Product Costs and Product List

For a 12′ x 8′ x 3′ pond ( Approx 1800 Gallons)

Pond liner (18′x14′) 170

Underlay 50

Submersible pump 140

Filter/UVc 160

Electricity Supply 150

Additional Plants 60

Selection of pond fish 60

Water conditioners/food/test kits/net etc. 40

Total: 830

The Pond’s Surroundings

A pond that you have spent many hours perfecting can still be in danger of looking out of context with the rest of the garden. Does your pond look as though nature would have placed it where it is? Is there easy access to view it? The finishing touches with a pond’s surroundings will be determined by the shape and size of the pond, whether formal, informal, raised or meandering.

Useful methods of blending a pond’s edges with the rest of the garden can include:

A gravel path to the pond which opens out towards the pond to sweep down into a pebble beached area. The path essentially becomes part of the pond.

Rather than edging the pond with a narrow ribbon of crazy paving, which may look a little contrived, why not try extending the area of the paving to form a patio for a natural viewing area.

Decking can also be used to link the house with the pond, giving the pond a fully integrated feel with the structure of the house rather than standing out as a structure on its own.

If using a specific type of stone for a rockery and waterfall, continue to use the same stone in the same proportions in other areas of the garden. Rockwork that is scattered to border paths or to help form a raised bed continues the theme, unifying pond and garden.

Pond improvement tips.

If in doubt when deciding whether to replace an old liner, it will prove a better option in the long run to fit a new liner. Better for your peace of mind as well.

If your inherited pond does surprisingly turn out to contain a few fish, rather than struggle to put them up in a temporary pond, ask if a neighbour will foster them for a few weeks in their pond.

If choosing a pond filter/UVc and pump for a pond, if the pond volume is an ‘in between’ size, always choose a large pump and filter than required. This will make life easier for you and give your fish better water quality.

When running in a new pond that has a new filter, stock the pond gradually with a few fish each week. Be as patient in stocking the pond as you have been planning and renovating it. In this way, your filter will mature in good time without water quality deteriorating and fish becoming stressed.

Kill blanketweed and string algae.