Pond in the new house you have moved into and bought

When I leaf through “Koi Ponds and Gardens” and see, amongst many other things, pictures of various koi pond projects showing ‘before and after’ scenes, I often wonder what it would take for those same koi keepers to consider moving house.

Even more so when taking into consideration the considerable financial investment as well as the many hours of blood, sweat and tears it has taken to construct the pond. I also wonder whether such a feature in the back garden could work in favour or against a quick house sale.

Either way, many koi keepers and pond owners do move house, which means that the new owners will inevitably inherit a pond. As it is likely that the new owner has no pond keeping experience, they are likely to be in two minds as to what to do with the pond. Likewise, if you find yourself in the position of being a new home (and pond owner), what are your options? And what do you need to know or do for you to be able to make the right decision? (which in my unbiased opinion would be to keep the pond!).

Let’s assume that the house purchase has taken two to three months to complete. When you viewed the house back in August, you remember seeing a medium-sized pond complete with waterfall, maturely planted with signs of a few shy fish in amongst the submerged weed.

The pond worked well with the rest of the garden’s layout and you looked forward to getting your hands wet and becoming a proud owner of a pond. However, it is now November. The water is no longer as clear as you remembered it, and the plants, although they are still there, are now brown and decaying in the pond. You feel quite let down and disappointed, so what are your options?

Keep it or fill it in? It would certainly be easier for you to fill it in, especially when you feel like you do right now. The safety of young toddlers is not a concern for you, but you should remember the dangers that a pond represents for any friends or family who have children. But thinking back to how pleasant the pond looked only a few months ago, you’re happy to rise to the challenge of returning it back to its summer glory, having obviously been neglected since the property went on the market.

The positive points in your favour are that the pond is obviously mature, well planted and has a sizable black box filter feeding a waterfall. It also looks as though the submersible pump is still present, complete with pipework to the filter. A pond with such essential assets is so much easier to retrieve than one that consists simply of a murky, stagnant water-filled hole in the ground.

Furthermore, by working with and exploiting the pond’s maturity, it should be no trouble at all to have your pond ready for spring and looking good again in the early summer. The mature aquatic and marginal plants will help to mature the water, offer cover and water conditioning attributes, while the pump combined with a UVc and filter will work as they did back in August to provide you with a balanced, restful aquatic oasis.

There will be a varying amount of maintenance each week, and daily interaction from March to September at feeding time. Who knows, with a little luck, you may even be able to add a few koi to the pond, but that will depend on a number of your pond’s existing features.

To help you get your newly inherited pond back to it’s August glory, you should consider the following 10 areas.

1. Water quality.

Even though in its present state your pond may look unsuitable for fish, you will probably be pleasantly surprised if you were to test it and you may even unknowingly already to be the owner of a few ‘hibernating’ pond fish. In order to establish whether your pond’s water quality is suitable for fish, you’ll have to purchase a few test kits. These will also help you through the first year or so with your pond and help you to confirm that your pond is progressing well after it’s spring clean. Providing your fish with the best water quality possible is the most you can do to ensure the health and longevity of your fish.

The test kits and results you should aim for are as follows: pH. stable, between 7.5 and 8.5 Ammonia. 0 Nitrite. 0 Nitrate. < 50ppm, but ideally <25ppm GH/KH. Showing that your water is hard and well buffered

You should test your water right away to see what your starting point is. In November, when your pond is inactive, you would expect ammonia or nitrite readings to be zero. I would not expect any of the parameters to be out of the desirable range, with it being such a mature pond, but you should confirm this none the less. If you are not sure what your readings mean, then take them into a koi dealer who will be more than happy to explain.

If you’re worried about green water, then your UVc and filter will soon clear things this spring. You may also notice beard-like growths of filamentous algae in and around submerged aquatic plants. This is blanket weed, and can be controlled in a number of ways, using your preferred pond additives (from chemicals that kill, control or reduce, to treatments that remove nutrients on which the blanket weed thrives).

Whatever you do, do not be tempted to completely empty your pond and refill it with tap water. Your pond will be harbouring (and benefiting from) a wide diversity of beneficial bacteria, and you should protect this at all costs. This diversity is arguably your pond’s greatest asset.

2. Maintenance.

If there is an obvious amount of leaf and plant matter in the pond then remove it carefully with a hand net. Take care not to dislodge any settled a sediment at this stage as this could turn all of your pond water foul and lead to fish health problems. Any untidy marginal plants can also be clipped back, bearing in mind that this is an ideal time to evaluate and look at re-potting your plants. If you don’t feel like doing it now, you’ve got until Easter. You also need to make a similar decision about tackling and removing any silt that may have settled on the pond bottom. The easy (but inadvisable) option is to empty the pond completely and start next spring with a completely new pond, complete with all of the running in an teething problems. I suggest that you hire a pond vacuum from your nearest pond store or koi dealer as this will remove the silt, and but preserve the maturity and invertebrate wildlife in your pond.

A good clue as to the integrity of your 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 the fabric of the pond 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.

3. Filtration.

As your filter will not be running at this time of year, you can clean the brushes, foams and other media, but do so with buckets of pond water. This will again help to preserve any residual bacterial maturity and diversity that you may still have in your filter. The filter and UVc should be suited to the pond’s volume, but if you’re serious about keeping koi, and the pond’s depth is adequate, this is an area that you may have to look at improving. As your existing filtration is pump-fed, it would make sense to continue with this set-up, but look at extending it. To convert to a gravity-fed filter at this stage would mean a complete rebuild. It really depends on how serious you are about keeping koi. A gravity-fed filter is the preferred method of filtering a koi pond, with clearly defined filter chambers, however, putting pump-fed chambers or specifically manufactured multi-chamber units for a pump-fed set-up could prove to be just as effective at maintaining good water quality.

As your filter will process and break down the toxic waste produced by your fish, it should be cleaned as soon as possible, ready to be brought online when the water temperature starts to rise above 6oC.

4. Pump.

Even though your submersible pump is present at the bottom of the pond, you should satisfy yourself that it is in full working order. This will also be a good opportunity to trace the pond’s electrics back to their source, inspecting that any DIY connections made by the previous owner are safe. It may also be wise to acquaint yourself with the route and that any cabling takes between the pond and house.

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.

And while it is out of the pond, turn on the power momentarily to check that the pump is operational. By turning it on in the pond, if there is a silt problem, you may disturb it or cause it to be circulated within the pond (which is something to avoid at all costs).

If your pump is not working, you will need to assess the size of replacement required. You can do this by taking the old pump to your koi dealer for a replacement, or if you are considering a larger filter system for some koi in the future you will need to calculate your pond’s volume and purchase a pump whose output (at the desired head) will be sufficient to turnover your pond once every two hours.

How to calculate the volume of your pond.

Measure the Pond’s width, length and depth (in ft) and multiply it all three measurements to calculate the volume in cubic feet. Multiply this figure by 6.25 to calculate the volume of the pond in gallons.


If you have inherited a garden pond it is unlikely to have included an air pump or diffusers. You should really address aeration if you are looking to add a significant stock of koi in your inherited pond. Things to consider will include your pond’s depth (as this will determine the size of air pump required as it will need to pump to the bottom of the pond). My preferred aeration devices for a koi pond are air domes as you require fewer than if you were to use air stones and they mix and aerate the pond water very effectively. Your pump-fed trickle filter will not require any additional aeration.

Other equipment. You also have an independent UVC in line between your pump and filter. This clears the green water, working in conjunction with the filter. The UV bulb will generally need replacing every spring. I prefer to install a new bulb each February or March as a new bulb will emit it’s best radiation when it is needed, in the first few months of the year. It may also be worth carefully removing the brittle quartz sleeve and cleaning it as required, to ensure the bulb can irradiate effectively the circulating pond water as it passes through the unit.

If you had inherited a koi pond (as opposed to a large garden pond) then you may well have inherited other koi pond equipment such as a water purifier. This will be wall-mounted in your garage or outhouse near the tap water supply. Water for top-ups is passed through this unit (which consists of a series of in-line pods or cartridges) to make it safe for the fish. The active media in the purifier cartridges has a limited life (measured in terms of gallons of tap water treated) and unless the previous owner kept meticulous records, you will not know the age or condition of the media. You may have to speak to the vendor for advice.

6. Power Supply.

When you investigated the pump, you will have tested and inspected the electrical connections and supply. Where there are junction boxes or separate switch boxes for the UVc (and other outdoor electrical equipment, such as garden lighting), then check these are still intact and watertight. At the source end, (in the house), satisfy yourself that there is a circuit breaker for safety when you are in and around the pond. Fortunately, as most equipment for garden ponds is relatively low wattage, you can plug them into your mains supply. If having converted to koi keeping you wish to add an electric heater, then depending on the wattage, you may have to wire an electric feed directly into your house’s consumer unit. If you have any doubts about the safety of your pond’s power supply, then seek an electrician’s advice (you will more than likely have one visit your new house after the move any way for small alterations etc).

7. Pond plants.

I would keep all of your pond plants as they will be the life and beauty of your pond (until that is, you are convinced you want to convert totally to koi). You will need to assess, tidy up and re-pot your plants before spring. As this will disturb any silt, it should be done after the pond has been vacuumed or spring- cleaned.

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.

8. Fish.

It may seem strange to leave fish until they penultimate item on the list, but there are so many other preliminary factors that need sorting out before discussing fish. As mentioned earlier, I am against completely stripping down your pond (and losing its maturity), preferring to leave your fish undisturbed until they re-emerge in the spring. This will enable you to find out what fish you have in your pond in its mature and balanced state and allow you, next spring, to contemplate adding more fish of your own choice. You may be content with the fish you find in your pond or having seen koi during various visits to your retailer, you may wish to add some of those also. At least by not adding any fish at this stage, you will not run the risk of overstocking your pond. Your fish will not need feeding until spring, once water temperatures start to rise above 8oC (get yourself a pond thermometer) and only then offer them a quality food, fed on a basis of a little and often. This will be the first time you will have seen the fish and if there are any signs of ill-health (fungus, fin rot etc) seek the advice of your aquatic retailer.

9. Other changes

required should you choose to go for koi. If having seen your fish in spring, and have been tempted to change over to a dedicated koi pond, then you should be aware of some of the key issues relating to your decision.

a. Pond size and shape. Your existing pond will be more than likely unsuitable as a dedicated koi pond. Such a pond will be 4-5 ft deep, steep-sided and filtered via a bottom drain-fed filter. Even though your inherited pond may have been responsible for giving you the koi-bug, it will need replacing and enlarging before you do make the switch. Use your existing pond as a training ground for seeing how much time a pond demands for maintenance, becoming fully conversant with water quality, fish health and feeding. As soon as you move up to the world of koi keeping, hardware and the koi themselves are so much more expensive, making any mistakes equally as costly. You will also have to satisfy yourself that a larger koi pond will work well in the existing layout of your garden.

In summary, an inherited pond has been the introduction to the world of fish keeping for many avid hobbyists. Equally, many inherited ponds have been filled in by new homeowners who have had a bad experience or overlooked the true potential of a garden pond. I think the most regrettable thing that a novice pond-beneficiary could do with an inherited pond is to rush into making a quick decision. Let your pond experience it’s first spring and summer and see what it has to offer before making any big decisions (your budgets are likely to be at their tightest shortly after a house move any way). This will give you time to plan so that should you wish to make any changes to the pond, they will be well thought through and they will not include any needless expense. At least by living with your inherited pond through its first season, you can truly evaluate what you have inherited. This will also give you time to see if the koi-bug does bite or if you are simply happy to work with the pond you have inherited.

10. Shopping list.

If you inherit an overgrown, murky pond with no equipment and no fish, what will you need to get it up and running?

Product Costs and Product List

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

Pond liner (18′x14′) 200

Underlay 60

Submersible pump 140

Filter/UVc 200

Electricity Supply 150

Additional Plants 80

Selection of pond fish 100

Water conditioners/food/test kits/net etc. 60

Total: 990

If that same neglected pond needed to be overhauled, how long would it take?

The work can be divided into weekend-sized jobs.

Weekend 1: Initial Pond Assessment Assess the integrity of the liner and waterfall Buy test kits and test the water. Remove and clip back any decaying plant matter. Vac the pond and have a general tidy up

Weekend 2: Pond Equipment Test Pump, UVc and visually check the integrity of cable connectors and switches. Seek specialist electrical inspection/opinion asap Service/clean pump, UVc and filter media

Weekend 3: Spring Maintenance Re-pot plants Turn on pump and filter Change UV bulb

Weekend 4: Spring checks Look out for fish activity, feed sparingly and look out for any obvious health problems (fungus, fin rot etc) Continue to test water, monitoring ammonia and nitrite very closely If space allows, shop around and add new fish (small specimens) 2-3 at a time.

Garden and surroundings.

If the garden is as neglected and overgrown as the pond, then it would be a good idea to clear the overgrown garden before tackling the pond. This will help to put the pond and garden in perspective and give your ideas as to how the garden could be developed in conjunction with the pond. Features in and around the pond that would need addressing together would include hard landscaping (choice of stone, decking etc) and the installation of additional electric work (for garden lighting and additional pond hardware).

Top tips.

Water quality. Do not completely empty your pond, as this will lose years of priceless and irreplaceable maturity that will keep your pond water ‘sweet’ and stable.

Maintenance. If you have inherited your pond part-filled (and you suspect a leak), top it up with a hose and leave for a few days. Also, watch out for a tell-tale tide mark that points to the pond having been at a set level for some time. This is where you should look for your leak.

Filtration. When your filter is up and running, never clean it out completely, but carry out maintenance on sections of different media to maintain filter maturity.

Pump. If you have to buy a new pump, make sure that it has sufficient power to turnover your pond’s volume while pumping up to the required head (through the given hose diameter up to the top of the filter and waterfall)

Aeration. Aerate from the bottom of the pond as this encourages excellent water mixing.

UVc. Change the bulb at the beginning of the season to ensure that it keeps on top of rampant algae growth early in the spring.

Power supply. You are likely to have an electrician visit your house for alterations after the move. Ask him to inspect your pond’s electricity supply.

Pond plants. If you do convert your pond to a koi pond, then don’t compost any surplus aquatic plants but seek a trade with your aquatic retailer.

Fish. If you inherit a pond in winter, don’t stir up your pond with a hand net out of curiosity to see what fish the vendor may have left but wait until spring for them to come out of their hibernation naturally.

Converting to a koi pond. If you’re new to fishkeeping, but feel the urge to keep koi, run with your existing pond for at least a season to gain experience while you plan you next pond and avoid costly mistakes with your koi conversion.

Kill blanketweed and string algae.