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How To Build An Outdoor Fish Pond

Posted by on Jan 26 2018

At CD Aquatics, we pride ourselves on our knowledge of everything fish! Therefore, we wanted to provide you with as much information as possible before you start caring for your very own fish. Here, we have devised a guide to building a variety of different ponds. We know that a pond can really make a garden look spectacular so we want to help you to do it correctly, and to optimise your pond potential.

If you want to know more how to build a pond, look no further...

Necessary Steps for Pond Construction

First of all, you need to decide which type of pond you wish to build, i.e. a wildlife pond, goldfish pond, or a Koi pond. If you plan on keeping Koi, there are different ways of running and filtering, which will be explained as you read on, so don't assume that all ponds will work the same.


Careful planning is required when deciding to create and build a pond. In addition to deciding on the size of the pond required, it is also important to decide on the location of the pond. It should be located where it can be easily viewed and where it will obtain sunlight for approximately 5-6 hours a day, although some shading over part of the pond is beneficial. This will help to promote good plant growth, also bear in mind that the more you expose the water to sunlight, the more likely that you will encourage algae & blanket-weed growth in the pool - which isn't a good thing in large quanities.

Also, bear in mind that trees can cause problems with ponds. Overhanging trees should be avoided, as falling leaves etc. will pollute the water. Tree roots could threaten the structure of the pond and some species of trees are poisonous.

In addition to deciding on the location of the pond, you will need to decide on the type of pond liner to be used, whether it’s going to be a flexible pond liner, a rigid pond liner, or built out of brick, and what features you require e.g. fountain, waterfalls, bridges etc. Once you have decided on the location and size of your pool, the next step is the equipment.

Possibly the most important decision is the equipment required for running the type of pond you wish to install. Once you have the size of the pond, you can then choose the equipment to suit it; the main requirements being a pump, uv steriliser and pond filter. If you're not sure on how to work out the gallons your pond will hold, which will then determine the size of the pump, UV and filter that you require, then just give us a call or email us, and we will be able to advise you - or see our ‘helpful hints’ page, or the glossary to help you choose the products that will best suit your needs.


Building a Wildlife Pond

What’s needed for the build of a wildlife pond?

A wildlife pond is going to be the cheapest one of all to install; the only thing you really need is the flexible PVC pond liner or rubber pond liner, or a pre-formed pond. If you would like a water feature or waterfall, you will require a pump. NOTE, if you do install a pump, you will need something with a fine filter on the inlet to the pump to stop any frogs, toads, tadpoles, newts or any other types of wildlife in the pond from being drawn into the pump. A good option for this type of pond are the Hozelock EasyClear all in one, these consist of a pump, filter and UV in one compact unit, an ideal choice for keeping ponds clean and free from green water, and that are not going to have excessive fish waste.


Aquatic Plants

They help to enhance the look of the pond and re-create the natural environment. Plants can also assist in the maintenance of the water quality. However, some plants grow very quickly and can take over the pond unless you periodically remove some of them. All new plants should be rinsed before you place them into the pond.
Aquatic plants must be placed in an aquatic plant basket with hession to stop the soil from coming out, this allows their root systems to receive a flow of water in order to supply sufficient nutrients and oxygen.


Aquatic Compost

It is important to use a specialist aquatic product for your plants. Ordinary soil or compost may contain contaminants that may be harmful to fish and other pond life. In addition, it is unlikely to contain the correct balance of nutrients required by aquatic plants, and may encourage excessive algae growth. We recommend Aquatic Compost.


Building a Goldfish Pond

A goldfish pond is the cheapest fish pond to install. As before, there are two choices of lining to choose from, flexible pond liner or a rigid pre-formed pond liner. The biggest difference between a goldfish pond and a wildlife pond is that you will want to see the fish you have put in. A pond pump is essential for creating water circulation and in most cases is also responsible for pumping water through the filter. The filter helps keep the water clearer by removing fish waste, uneaten food and organic debris that would otherwise pollute the water. The pond filter is also home to millions of beneficial bacteria that remove toxic ammonia and nitrite from the water. Therefore without the filter, water quality would be compromised. So, for this one, you will require a pond pump, pond filter and sometimes a pond UV which will help keep green water and blanket-weed away.

If a filter, waterfall or stream is required, make sure the pump has an additional outlet to supply water to them as well as the fountain on the pump.

There are different types of pond filters on the market, some combining all three things together i.e. All in One pump, UV and filter, which is positioned in the pool itself. The other types of filters are positioned outside the pond, they are pressurized filters or pump fed filters whereby the water from the pool is pumped to the filter and then returned to the pond directly, or via a waterfall by gravity.

Both of these pond filters can come with the UV steriliser or a UV can be fitted later on if needed, though most ponds will need to have one fitted. We recommend the TMC (Tropical Marine Centre) range of UV’s or the Hozelock range - both are good units. When using a pump, UV and filter, please make sure that the pond pump is within the flow rates of the UV and filter, as getting this wrong will have a dramatic effect on how well your system will work. If you're not sure, please give us a call, and we will be happy to discuss your requirements.

These items go together as follows :
The pump is placed into the pond with a piece of flexible hose fitted to the pump and secured with a jubilee/hose clip, the other end of the hose is connected to one end of the UV, and another piece of hose needs to come off the other end; both ends must have hose clips fitted. Take the hose that comes off the one end of the UV to the filter, and again fit a hose clip. The outlet from the filter will go directly back to the pond, or if fitted, down a waterfall.


With safety in mind, always get someone who knows what they are doing to install electrical appliances. When using anything which runs on electricity, it’s best to run one feed to a safe place near the pond where a pond safe switch box can be fitted. These are individually fused and have neon lights to show that they are working OK. You can also fit a power safe trip switch onto the feed to the power safe box.

Tip : however many electrical appliances you have, always allow one extra outlet; you may wish to add something extra at a later date.


Building a Koi pond

When you have decided on the location of the pool and the size, as mentioned before there are different ways of lining the pond, and they are flexible liners, PVC or Rubber. And the other way is to build the pond out of brick. If you choose the brick option, then you will also have to render & seal the brick work to retain the water with products such as, Clear G4 pond sealer or Black G4 pond sealer, or fibreglass. You will also have to decide on how you are going to filter it. And yet again there are choices i.e. whether it’s pumped fed, or gravity fed.

A pump feed Koi pond or any type of fish pond will have a lot more maintenance when pump fed, compared to a gravity feed. Also, the cost of having a pond with lower maintenance does not cost that much more to install. The main difference is a bottom drain, and the size of the pipe joining the drain to the pond filter system, you still need the same size filter, UV and pump. If you do decide to use gravity, you have a lot of options and choices with the water return. Lets look at these two choices in a bit more depth.

A Koi pond pumped fed filter system comes with a lot more maintenance, and are harder to look after. Once you’ve chosen the size and location of the pond and what type of pond liner you're going to use, whether it’s a flexible liner or brick type; after creating the pond, you now have to look at the filtration side. You will need a pump, a UV steriliser and a filter.

If you choose a pressurized filter, this can be positioned at any level to the water level in the pond. The water is pumped from the pump through the UV into the filter, then back to the pond directly or down a waterfall. The Hozelock Revolution pressurized filters are highly recommended. They are extremely easy to maintain and are very efficient; available as the Hozelock Bioforce Revolution Kit, complete with the pump which ensures you have the correct size and flow rate - or you can purchase just the Hozelock Bioforce Revolution Filter on its own without the pump.


The outlet from a box filter is usually bigger than the inlet; this is so it doesn’t overflow, which can not happen on a pressurized filter.


A gravity feed Koi pond is without a doubt the best way to run and maintain any large fish pond, and has many other benefits. However, it is not really feasible on smaller ponds, as small filters are unable to accept a large inlet; we recommend a gravity fed system for 2000 gallon ponds onwards. When you have decided on the location of the pool and the size, as mentioned before, there are different ways of lining the pond, and they are flexible liners, PVC or rubber. And the other way is to build the pond out of brick, which has to be rendered and then sealed to retain the water with such sealers like G4 pond sealer, or fibre glass.

The first stage is to mark out the site and decide where the pond filter is going to be housed. You also have to know the height of the water level in your pond, so that you can set the height of the filter the same, without this, the system will not work. You then fit a 4” / 110mm solvent weld (glue fit) bottom drain in the middle of the bottom of the pond. If a pond liner is used, always use silicone sealant to seal the liner. The bottom drain will act as a feed to your filter and at the same time, keep the floor of the pond clean from fish waste & debris.

A good point to remember : there are two types of 4” pipe, and they are the 4” pressure pipe and 4”/110mm waste pipe; both are solvent weld. If using a 110mm bottom drain, you will need the 110mm WASTE fittings and pipe system. If using a 4" imperial pressure drain, you will need the 4" IMPERIAL PRESSURE fittings and pipe system. Never use 4” ring seal pipes under floor, you can never tell if they are sealed properly until you fill the pond up and by then it’s too late!

The outlet from the drain will go directly into the first chamber of the filter, unless a vortex chamber is fitted. The vortex acts as a settlement chamber, and will catch most of the solids that come from the pond, which can be flushed away to waste. Always fit a pressure gate slide valve if using an imperial pressure pipe system or the 110mm waste gate slide valve, if using a solvent weld waste pipe system, or ball valve, we stock both imperial pressure ball valves and waste ball valves to the inlet pipe from the bottom drain, where it goes in the filter or vortex, if fitted. This allows you to shut off the water from the pond when you do any maintenance.

When the water enters the filter, it will go through several chambers, this is why it’s called a multi-chamber, or multi-bay filter. These consist of different types of filter media; such as, filter brushesflo-corblue matting (jap-mat), k1alfa grog or as some people call it volcanic rock, bac-bio balls, bio-flobac tubes, zeolite, ceramic media, foams or filter pads, most of this can be put into filter media sacks so the media can be taken out easily for maintenance.

Once the water has gone through the filter, it will go through a submersible pump that is fitted into the last chamber of the pond filter or alternatively, you can fit an external pump outside the filter on the opposite end to the inlet end. After the water has gone through the pump, it will go into the UV then back into the pond, however you wish to return the water. Another good thing to fit is venturi, which is fitted on the inside of the pond where the water is passed through and air is drawn down a pipe and mixed with water giving a good supply of air into the pond at no extra cost. The only other way to do this is to install an air pump, air line and air stone.

Other things that can be fitted are things like pond skimmerspond heaters, pond sieves, pond lightsair pumps and air stones, and waterfalls.


*Always get someone who knows what they are doing to install electrical appliances.*


When using anything which runs on electricity, it’s best to run one feed to a safe place near the pond where a pond safe switch box can be fitted. These are individually fused and have neon lights to show that they are working OK. You can also fit a power safe trip switch onto the feed to the power safe box.


Tip : however many electric appliances you have, always allow one extra outlet in case you want to add something extra one day.


Useful things to have around :

Handling Net - this may be useful for handling fish and removing debris from the pond.

Tap Water Conditioner - to remove chlorine, chloramines & toxins (which are harmful to fish) from tap water.

Filter Starter - to help start up your filters, new or old

Test Kits - to periodically check the levels of ammonia, nitrite and pH in the pond water. There are a wide variety of test kits available.

Fish Food - always buy good quality foods for your fish; cheap food is no good for your fish, your filters or your water quality.

Sump pumps - these are good for moving large amounts of water quickly. 

Koi Viewing Bowls - just in case you have a sick fish, you can treat them in the viewing bowl away from the rest of your fish.


We hope you find all of this useful when starting to build a pond for your own garden. Whatever type of pond you decide to build, we have the advice and equipment you'll need right here at CD Aquatics. Now that you know how to build a pond, browse our pond supplies today!

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