Designing & Planning – Pond construction

You have a choice of either using a liner or concrete blocks with your new pond and render it using fibromix, or render it and then coat with fibre glass. It is recommended that you use butyl if you choose to use a liner as it will give you durability, even though it is pricier.

You should purchase a box liner which can be made up to the correct shape if you choose to construct a formal shape pond (make sure you have your measurements correct then it will fit with a minimum of creases or folds).

Liners however can be pierced by sharp instruments, although it does seem like an unlikely problem that members have suffered. Make sure that you are aware of the quality of the liners, and get plenty of feedback and recommendations from koi enthusiast who do have experience with using liners in their ponds. Buy only from reputable dealers to make sure that the liners are not toxic to the fish.

Before you stock the pond with fish, make sures that you wash out and clean the liners carefully. This is also applicable to ponds constructed with fibreglass and rendered ponds. Fill out the complete system (without the filter media), circulate it for a few days then clean it out. Refill after before you actually start stocking the fish in the pond.

Fibreglass coating

You should seek professional help if you decide to apply fibreglass to your pond. Remember that not just about anyone who’s repaired or built fiberglass would be qualified to coat a pond with it. Experience counts and employ workers who have had experience lining a pond with fiberglass.

Used for car bodies and boats, fibreglass is toxic to fish. To be able to use it for the pond, it has to be neutralized. The people you employ to apply this coating must be made aware of this, and must have had experience in the application process as well.  Feed back from previous customers will help you decide whether you should employ them or not. There are also other factors that you should look into, like what you should look out for when doing repairs, or when you need to do alteration to the original coating. Discuss this with the original installer before you proceed with the project.

Once the coating is complete, allow it to dry out completely before you start using it. Check the surface for integrity, especially in the corners as there are often sharp edges which could damage cause injury to the fish. These should be smoothed off.

Filter capacity

You must know the exact volume of your system so that you can choose the correct filtration system (types will be discussed in following chapters). Filter capacity and pond capacity are two separate matters on its own.  There may be an instance where you will decide to just treat your pond, so knowing the gallonage of the pond on its own will be required, as the capacity of the pond will not likely change. The filter capacity though, can change when you alter the media. The correct gallonage must be known, especially when using chemicals during treatments.

Actual Pond Volume

Below shows the calculation on the volume of your pond

Actual Pond Volume (US gallons)

=average length (ft) x average width (ft) x average depth (ft) x 7.48


Pond is 12\’ avg. length x 10\’ avg. width x 2\’ avg. depth

Pond Volume: 12 x 10 x 2 x 7.48 = 1,795 US gallons

Effective Pond Volume

When selecting the proper size equipment for your pond, you should not depend solely on the actual volume alone. You will need to calculate the effective volume of your pond. This value is influenced by various environmental factors, such as direct exposure to sunlight, shallow depth, or climate conditions, THEN add to the actual volume by the factors listed below:

Average pond water depth is less than 2\’ 6″: + 25 %

Pond is located in full sunshine: + 25 %
Pond is located in subtropical climate (e.g. Florida): + 35 %
Pond is located in temperate climate (e.g. Eastern Seaboard, Southern U.S.): + 15 %
Pond is located in Northern climate: + 0 %


    You have a 2,500 gallon pond that is 4\’ deep, located in full sunshine and you live in a Northern climate.

    The effective volume of your pond is 3,125 gallons (2,500 + 25 %).

    Allowance for Fish Stocking Level

    So far the information above is based on a fish stocking level of not more than 100″ of fish per 1000 gallons of pond volume. There would be a pro-rata increase in the size of all equipment if there are any variations in stocking level above this number.

    So, a 2000 gallon pond stocked at 150″ of fish per 1000 gallons will require equipment appropriate for a 3000 gallon pond, i.e. 50 % more fish requires 50 % greater equipment capacity.


    Get a rough estimation of the materials that you will be using during the construction of your pond. This way, once you have a rough estimate, you should be able to negotiate for a discount with suppliers and should be allowed to do this even though you will not be purchasing all materials at the same time because you would not have enough space on site to store them.

    Check also on the cost of delivery, so that you can maximize efficiency during that process (delivery). It would not make sense to pay for a hugs truck to deliver a small load at the wrong time (when one part of the construction hasn’t been completed yet). This could mean that you would have to store the extra materials on site, exposing them to decay when they are left too long on their own.

    Cost is often calculated on below one ton and above one ton being considerably more. This could mean a high variation in cost, and a large sized pond will require at least about 6 to 9 skips, once you also take into account the need to rid of the soil you dig out.


    Once you’ve decided on your final layout, it is time to start marking out the ground to get an idea of the actual size of the pone. This is because what’s on paper may differ greatly once you’ve implemented it in the field.