Ornamental Fish Ponds
one of publisher and bookseller InfinityJunction.com's ultra-mini guides to petcare
by the Infinity Junction editor in chief, Neil Gee
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In this article -
the editor's fish pond   
  • 1 - why bother
  • 2 - design considerations
  • 3 - a neglected pond
  • 4 - setting up a new pond
  • 5 - plants
  • 6 - algae & blanket weed
  • 7 - fish
  • 8 - food
  • 9 - winter
  • 10 - further suggestions
  •   water lily - close-up

    1 - the Peace of Ponds
       One of the nicest things on a warm summer evening is to sit in dappled shade of surrounding vegetation and just gaze and contemplate beside an ornamental fish pond. And if the pond has colourful fish, a tinkling waterfall and nice plants surrounding it, it's easy to find oneself transported away from the bustle and stress of modern life into a world of tranquillity and peace. So, to invest a few hours setting up and maintaining a pond in your garden, or on your terrace or patio, is often well worthwhile. And if you do it right, it won't be that awful mess of green slime you sometimes see in city gardens, instead it will be a centrepiece to admire and be proud of.

    2 - Starting from Scratch - (think first)
       Assuming you don't have an estate of acres and staff to match, don't be over-ambitious. A pond of just a couple of hundred gallons (1000 litres) can look terrific in a typical town garden and have a healthy ecosystem too.
       And you don't need to dig it very deep or raise it very high: a pond of 40cm (16 inches) is sufficiently deep for small and medium sized fish, water lilies and many other attractive aquatic plants. Indeed for marginal plants such as cotton grass you would need a shelf around part of it much less than this, typically only 4 inches are needed (10cm) - however if it is deeper it will give you a wider choice of plants, but you'll have to raise bog garden plants on a brick or similar so as not to be too deep.
    SAFETY WARNING: ponds, especially sunken ponds, are not a clever idea to have in your garden when there are young children around. It is possible for an adult to drown in just 2 inches (5cm) of water, so it must be even less for toddlers, and infants often have no idea of what is dangerous and what isn't.

    2a) - types of pond
       There are two most common types of domestic garden ponds- those with a pre-formed 'hard' moulded liner, and those lined with flexible butyl rubber. These days it really isn't worth building a cement lined pond because it can take a bit of effort to stop it leaking after it has set and shrunk, and needs months of filling and emptying to be certain the lime residues won't kill your fish.
       For overall safety of your fish, the pre-formed hard moulded types are more reliable as it's much more difficult to puncture and spring leaks. Yes they cost a bit more, but it's worth paying the extra. Both these types need to be placed in a thick layer of soft sand or thick old carpet inside their containment to ensure they can't be squashed against sharp stones etc when filled with water.

    2b) - where to site a pond
       Fish ponds don't like to be in permanent full shade because the oxygenating plants cannot get enough light to do their necessary job. But it also isn't good to have too much sunlight because it tends to encourage algae to bloom and this can have a detrimental effect both on the health of the ecosystem and the appearance of the pond. Now, you can get around full sun by planting shrubs nearby or constructing trellises or pergolas to provide partial shade in summer when plants come into full leaf and when the pond needs most shading. You can also employ the use of shade-providing aquatic plants- however be aware that, in temperate latitudes, most ornamental (exotic) water lilies etc do not come into full leaf until after the main season for the start of algal bloom has started.

    2c) - raised or sunken?
       Sunken ponds look more natural and are often cheaper to build, however they are also much more likely to get contaminated by muddy rainwater, dead leaves, drowned animals and the like. Raised ponds need a strong enough structure to support them and may not attract frogs etc, (if you want that,) unless there is a vegetated ramp etc or they are built into a sloping bank where only part of it is raised.
       There is one major advantage of raised or partially raised ponds and that is you don't have to be reliant on expensive submersible water pumps to circulate and filter water. If you use a hard liner, simple domestic plumbing can be used and an ordinary central heating pump bought at only a fifth of the price for equivalent power. They last just as long if installed in a suitable weather-proof housing and are much easier to get at for maintenance. (NOTES- 1: you cannot use a standard rotary water pump above water level because they need top pressure to work. 2: if you pierce the liner, do not do so right at the bottom in case your joint leaks; an intake to the pump, such as the fitting used to fill a lavatory cistern, should leave enough depth of water beneath it so that fish can survive after seal failure. 3: a grid or mesh filter on the water intake will stop baby fish, tadpoles etc from being sucked in and also protect the pump's internal rotor from damage by debris.)

    2d) - moving or static?
       With very few exceptions, smaller ornamental fish ponds should have some sort of water movement, either natural from a stream, or more likely via an electric pump, (see above.) This is even more important if your pond gets a lot of sun, as this tends to encourage all sorts of bacterial, fungal and algal growth some of which is undesirable. Ponds less than about 100 gallons (500 litres) need water circulation more than those twice the size or greater, simply because small ponds are unlikely to support such a diverse ecosystem as would keep them naturally clean.
       Having a large volume of flow compared to the pond volume, such as (for a 1000 litre pond) from a central heating pump or decent-sized submersible pond pump has enormous benefit over the rather pathetic fountains often purchased by inexperienced home pond makers. If you can achieve a turnover of at least several complete water changes per day, the chances of keeping your water clean and free from blanket weed etc are many times greater than if it takes a week to circulate the whole pond.
       Don't forget you'll need to clean your pump occasionally, so a way of removing it without the water escaping is needed from the start. The rotor housing of most pumps can be dismantled and the input, output, chamber and rotor should all be thoroughly cleaned and any hard deposits carefully scraped off.

    2e) - pond shape and depth.
       The actual shape of a pond doesn't matter much, except fish can escape from predators easier in a pond which is not too long and narrow. To avoid land animal and bird predators the pond also needs some depth. Ornamental ponds should not be too shallow for aquatic plants to grow well. Also ponds that are too shallow tend have high light levels and can warm up so much that algae growth is encouraged- see further below.

    2f) - filtered or natural?
       A good idea with smaller fish ponds is to include some sort of filtering for the water. The filter can do a number of vital things - firstly it allows bacteria, which break down fish faeces and other contaminants, to work vastly more effectively than they could do in a static pond. Secondly if combined with a waterfall or similar, it allows potentially poisonous dissolved gases such as ammonia and carbon dioxide to escape into the air and additional oxygen to be absorbed when its level in the pond water is low.
       The size of filter needed depends on your pond conditions, including how many fish you expect to have and the flow rate of your circulation system. Large expensive filters are not usually necessary for small domestic ponds with just a dozen small fish, indeed you can often improvise a filter from a large plastic container and basic filter medium which by itself is not expensive. Don't forget that smaller filters need to be cleaned more often. If you find your filter clogging quickly, then the water is too contaminated with solid matter and the bottom layer of water needs to be syphoned or pumped out along with most of the muck. As long as you don't take out more than 20% of the total volume in any week, then clean (tap) water can be run in without harming fish, (assuming the temperature difference is not great and the water not over-chlorinated.)
       A new pond would do well to have pre-conditioned filters installed; these are laced with useful bacteria and can get your bio-filter off to a flying start. Alternatively, if you know someone who already has a successful pond filter running, you could ask them for a small piece of their filter material in exchange for a new piece and place this in with your new filter to 'seed it' and speed the process of seasoning the filter.

    frog looking out from under water lily leafiridescent blue dragon fly
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    ponds can attract wildlife - frogs and many other species, like this blue dragonfly

    3 - Sorting Out a Neglected Pond
       You bought that house you fancied; it's got a pond; it's all clagged with blanket weed or you can't see any fish through brown murk, even though the sellers said there were some. What do you do?
       Basically it's salvage what's worth having and chucking out everything else time. Start siphoning or bailing until you come across pots of plants, submerged pipes, fish or whatever.
       The fish should be caught using an aquarium grade net (fine soft mesh) and put in a very large container of pond water. Over a period of days, (not hours,) you can replace no more than quarter of this container's volume with clean (best un-chlorinated) water, which must be at a similar temperature, once or at most twice a day, until the water is completely clear and you can examine the fish. If you have an aquarium air pump, bubble the water to keep it moving and oxygenated. Feed the fish with goldfish food or similar while they are in the transitional tank. If you see any sign of disease, treat it accordingly and do not put the fish back in the pond unless completely cured. Seriously diseased fish should be isolated from the others in a separate tank.
       Pond weed should be discarded if straggly or badly covered in blanket weed. (CARE- some types of pond weed can kill other plants if dumped on top, bin it or give it away to another pondy, don't leave it on the lawn for long.) Water lilies should be rinsed thoroughly and freed from all other weed and contamination, dead leaves cut off and then the lily must be kept wet (not just damp) at all times. If this is done in winter and the corms are large and sprouting in more than one place, then the corm can be cut or pulled apart to make new plants. Lightly contaminated aquatic plants of all types can be rinsed, blanket weed pulled off by hand during the process, and then placed in a bucket or tank of pink potassium permanganate solution for an hour or so. (If you accidentally add too much permanganate and it goes purple, only treat the weed for a few minutes, then place in clean tap water - do not let it dry out. Keep oxygenating weed in clean water, in sunlight to get it growing until it goes back in the pond.
       Drain the pond entirely, brush obvious growth off the sides and swill it out with clean tap water a couple of times, taking the last dirty water out with a sponge or similar - do not use disinfectant, bleach, or other cleansers as they can cause long-term contamination.
       If the pond had a filter this should be emptied and the container roughly cleaned without chemical cleansing agents and allowed to dry out. The filter medium should be squeezed empty of water (but not stone dry,) if badly clogged it should rinsed and teased into an open structure, then left outside in shade (unless freezing) to oxygenate for a few days depending on temperature, preferably a couple of weeks in winter; this will kill unwanted anaerobic bacteria, which can cause a pond to go foul with poisonous hydrogen sulphide. You should be able to use it again to 'seed' a new filter with useful bacteria. All pipes, pumps and waterfalls or fountains should be emptied, cleaned and dried as best as possible..
       Now go to the next sections...
    Coming in the next few months from Infinity Junction: The Pond Builder by Neil Gee - a very different slant on pond building! (A black comedy.) Check the book list at Infinity Junction
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    4 - Starting a New Pond - actually doing it
       You've got a stable and level-edged pond liner nicely bedded-down in thick protective sand in a good, safe position in your garden. Yes? If no, then get it before you go any further.
       If you are going to keep fish, in the deepest part you need to make a hiding place for them to escape to, eg from cats, bird predators etc. This should be large enough and stable enough to be a truly safe haven. Old ceramic drain pipe laid on its side often suffices, and if you can find square-section type, (like old fashioned chimney liners,) this will also allow you to place potted marginal plants on top of it, if not too deep.
       Set up your water filter and circulation system taking care to follow safety instructions, and also your waterfall or fountain if employed.
       Decide where you will later put plants, preferably potted, and make sure the depths are right for each plant. Checking this before you fill the pond, with the same size pots you expect to use, will save time and trouble later. Do any finishing work such as edging stones etc before filling so that the water can't get contaminated with mortar etc. Clean up dust and dropped excess material carefully, leaving the pond liner uncontaminated.
       When you have sorted everything that's going to be too deep to fix later, or at too long a stretch to do without wading, then you can fill the pond. Ideally you would use un-chlorinated sterile water, but since such a thing is usually unobtainable in the quantities you need, just use chlorinated tap water and leave it circulating for at least a week, (longer in cool weather,) before introducing plants. During this week you can adjust the waterfall to get the most pleasing effect, both visually and the sound it makes. If you use lights, you can also adjust them at the same time.

    5 - Plants
    salvinia rotundifolia (red)   One of the best methods of coping with pond plants is to keep them in pots: that makes them much easier to move around or bring out of the pond for trimming of dead stems and leaves, etc. Oxygenating weeds that grow proper roots (most of them do) are best potted into soil, (not compost or peat,) but to stop the soil turning the pond cloudy, a dense layer of moss can be used in the bottom where the holes are, and a layer of heavy pebbles placed on top around the stems. Don't use aquarium sized filter shingle because fish will move the little stones and disturb both soil and roots - something in the region of 2cm diameter (approx one inch) or even a bit more would do.
       A very good oxygenator, which is also both common and pretty tough once established, is elodea - 'Canadian pondweed' variety is the toughest. Plant more than you think you need to start off with because fish have a habit of uprooting it until its root system is properly grown. It's hard to have too much of it and you can always cut it back a bit if necessary.
       Larger plants such as water lilies sometimes develop pretty big root systems, well beyond their original pot, and these can be covered in a layer of soil, in turn this is also covered with stones to stop fish disturbing it. Until fish start to fertilise plants naturally, purpose manufactured slow dissolving (low nitrogen) solid fertiliser pellets can be used, but sparingly: you don't want the chemical content to be unpleasant for fish or cause unwanted algae growth.
        In a temperate spring, water-weeds need at least a couple of weeks to get over the shock of being re-planted, and ideally a whole month to establish themselves and be strong enough to resist the curiosity of fish.
       Floating plants can also be useful for reducing light levels in a pond and thus helping to keep algae to a minimum. There are many dozens of varieties from humble duckweed, through rampant water hyacinth, to brightly coloured salvinias, (pictured.) (Last two not hardy in cool temperate climates, so keep some in a bucket indoors to over-winter.) And there are varieties of plants which don't permanently root, but sink in winter and float just beneath the surface in summer; such as hornwort.
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    6 - Algae and Blanket Weed
       The bane of many a pond owner are various forms of algae. Two of the worst are that green/brown bloom which swamps a pond in certain conditions and makes it so murky that you cannot see your own finger when submersed, and the dreaded blanket weed, which ties up everything with millions of tiny green strings. The problem is, once well established it's very difficult to get rid of blanket weed without hard work. (See further below for suggestions.)
        Algae like warm water, sun, and plant fertiliser. They don't like a very highly oxygenated water. Keep the pond sufficiently shaded and the algae cannot thrive, one way is to let water lilies grow big enough to create natural shade. Also allow your oxygenating weeds to grow really bushy and spread out: as soon as the sun shines they'll start killing free-floating algae. Just make sure there are plenty of free passages for fish to swim around. Avoid having a pond right next to a warm wall or in hot sunlight. Once your plants are growing well, reduce nitrogen and fertilising minerals, if necessary by a slow water change.
        There are various algae killing agents, but experience shows that some of these cause as many problems as they solve, for example those based on permanganate and a flocculating agent, leave a thick foul sludge in the bottom of a pond which must be removed for the safety of your fish. One of the safest ones which actually does anything useful is dimethylurea, often available in mineral blocks which dissolve slowly. This too can cause a sediment, but not so rapid nor so foul. (Note: blocks containing dimethylurea should be of recent manufacture as they becomes less effective with age.) The earlier you tackle algae, the easier it is to control - as soon as any sign of green or brown cloudiness appears, treat the pond.
       Do not put fish into a pond with very high algae concentration because at night the algae can starve a pond of oxygen.
       Blanket weed is most effectively reduced by pulling it gently out by hand, trying not to pull up the wanted plants. It needs to be done regularly because it can restrict the movement of fish and if really bad can even trap them - get your arms wet! For areas you cannot easily reach, or if you don't want to dip your hand in the pond, get a straight stick and cut a groove in the end. It should be light and as long as is convenient, with the prong tips very roughly 2cm apart, (1 inch,) and with a clear gap at the ends of about 1 cm, then it can be used to penetrate the blanket and then slowly wind it round and round until it is caught. Lift or pull it out carefully to avoid uprooting or breaking wanted plants. You can go on doing this for hours in a big pond- some people find it therapeutic; the pond certainly will. By the time lilies and other light-shading plants have grown, you'll have to do this this less and less.
       Only if your pond has no fish, you can help reduce algae by using a special black dye to cut down sunlight. This also makes the contrast between water and floating/marginal plants seem greater but will reduce submerged plant growth and can harm wildlife.
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    7 - Fish
       Most important - don't be impatient and put fish in your pond before it's free from chlorine and all building residues, the water must be clean and the plants bedded in securely and producing oxygen in daylight.
        There are dozens of fancy fish breeds available in aquarium shops and pond centres. Unless you really know what you are doing, stick to the resilient old favourites. For the climate here at Infinity Junction (north-west England) red comets, shubunkins and orf are pretty tough. Fancy carp will also survive, but since these tend to be pricey to buy, you would be better to get your pond set up and thriving for a couple of years before you try them.
        And then there are bottom feeders etc. To be honest, you really need a largish pond and to have a bit of experience before using these.

    8 - Food
       After some months, a larger pond may supply fishes' nutritional needs from its own ecosystem. However, it's more fun to feed them and watch them come up to the food. If you want this to happen, you'll have to feed them a little every day until they get into the habit. Depending on the size of fish, you can use ordinary goldfish flakes or pond-fish pellets. Don't give them too much at once because food may go uneaten and start to go rotten in the pond. Fish really do better with occasional live food, in a large well established pond you won't have to worry, but in a newish pond, occasional bags of daphnia etc will help keep fish healthy.
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    9 - Winter
        In cool temperate climates ponds usually go inactive during the coldest winter months. Depending on the type of fish and the amount of daylight shining on the pond, very roughly when the water (not air temperature) drops continuously below 8C the weed will stop growing and the fish stop feeding actively. You still need to monitor the pond for various reasons. First, fallen leaves can form a stagnant layer at the bottom of the pond, which if left for long can rot and produce very toxic hydrogen sulphide gas which kills fish and other animals. Remove as much leaf debris as you can in autumn, including sunken lily leaves. Second, ice can form on top and if left for long can allow build-up of poisonous gases and not allow sufficient oxygen into the water for the fish to survive. Leaving the circulation pump running will help, but even then you may need to help it by taking an inch (2cm) of water out from beneath the ice layer, and carefully puncture a hole or two to allow air to get at the water surface. Third, sudden winter warm spells can make fish hungry, but with no food supply they might starve - try feeding them a little, if they take it, feed a bit at a time until they lose interest. Try this every day when the weather is mild.
       Do monitor fish regularly: at lower temperatures, if any do get ill, their metabolism is often too slow for their own immune response and physical healing processes to work properly. If necessary bring injured or sick fish into a slightly warmer environment to treat them, eg a tank in your garage.
       Winter is also the time to check water plants and remove blanket weed. Cold weather often has a clearing effect on small ponds: algae and bacteria grow too slowly to be a cause of cloudiness. It makes it easier to see what you're doing. Also splitting or transplanting is much less harmful when plants are dormant.
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    10 - Further Suggestions
    Cotton Grass    10a) - Have your pond overflow into a separate bog garden at the water's edge; the choice of suitable plants is enormous, from giant dark red lobelia, through a host of fancy grasses, (cotton grass pictured,) rushes and even could include delicious wild strawberries just above water level. Don't forget to top up pond water levels to keep the bog garden wet.

       10b) - If you suffer from cats or herons trying to get your fish, lay green synthetic netting, or string brightly coloured cotton thread over the pond when you're not there. You can support it on a simple bamboo framework if not too big, or hook it onto anchor points around the pond - being dark green, you'll hardly notice netting at a distance. With smaller ponds, you can use tall pampas flower stems stuck into the ground to make landing impossible for herons.

        10c) - Plant a wind-break or visual shelter around your pond, possibly with an opening out of sight of the neighbours, to make the pond area into your secret den.

        10d) - Buy or make yourself a comfortable outside chair or bench, not one of those cheap back-breakers, a really comfortable one. Put a small table or ledge somewhere nearby and sit there with your glass of wine, ice-cold beer, mineral water, or whatever else you fancy. Just forget the telly and the office and dream your own dreams.

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    * Duckweed, very small but frequently numerous pale green leaved plants, can be a nuisance because of the rate at which it can spread and cover the whole surface. Many pond owners hate duckweed. If you need to get rid of it, this is a long job unless you start your pond afresh. The best way to get rid of it in an established and otherwise healthy pond is to take all potted and marginal plants out because they can harbour duckweed without you realising. Hose these down with water on land that won't drain into the pond. If you do this in cold weather (eg a temperate winter) you can let it dry out a bit which will help kill any remaining duckweed around the roots and lower stems- DON'T let water lilies dry at all or you'll kill them. When ice forms, sheets of trapped duckweed can be lifted out then removed. You won't get it all out like this but it sure helps. Then you can use aquarium nets to lift duckweed plants that are not attached to other plants. After that it's a very tedious job of picking the rest out by hand. You can spread this over several sessions, gradually clearing area by area. Even after that you'll find some has managed to hide itself amongst other plants etc, so you'll need to be vigilant for quite a few days after the last visible duckweed plant appears to have been removed.

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