Converting a Swimming Pool to a Koi Pond + a Gravity Fed Filtration System

Miss Piggy



Swimming Pool to Koi Pond Conversion

The Gauteng Chapter of the South African Koi Keepers Society had a Pond Safari to the home William Kelly and Wendy Kelly.

The Gauteng Chapter would like to thank William and Wendy Kelly for hosting a Society meeting at their home. Mark from Happy Koi and his wife Susi were also working feverishly behind the scenes to get everything organised.

A very big thank you to William and Mark of Happy Koi.

Society members were very interested in looking at the gravity fed filtration system William had installed on his swimming pool/koi pond.

The first order of business was some announcements relative to the Society and then the floor was given to William to describe in detail how he had converted his swimming pool to a koi pond.



Chris Neaves, William Kelly, Maria Anna Botha

(Everyone taking the Chairman seriously)



(Koi keepers listening to the talk on the koi pond)



The Basic Design

A 60,000 rectangular swimming pool was used. At the deep end holes were drilled through the shell to install 4 x 110mm bottom drains which feed the water to a discharge box. Concrete was poured around the drains and everything sealed.

The sides were raised and this resulted in a volume of 80,000L. The outer walls of the swimming pool were raised 500mm and an additional extension on the side adjacent to the boundary wall was added to allow for a plant shelf to be created to soften the wall and create some focal interest on the pond.

A large discharge box was built which served as a surface skimmer. This was to overcome the leaf problem form the overhanging oak tree.




The Filtration Sysyem

The filter system is a gravity system. The water is moved from the bottom drains and the large surface skimmer to a two-stage settlement chamber. The first stage comprises of the four bottom drains and a large cut away section direct to the pond which draws surface water and therefore acts as a surface skimmer. This is shut off by using a stainless steel plate William had made specifically for this purpose.

There is a leaf problem created by a beautiful, large oak tree in the neighbours garden which has grown right on the boundary wall and therefore overhangs the pond. The basic design had to accomodate th eleaf problem. So the skimmer and discharge box are designed with large leaf traps and large skimmers. William mentions that in autumn so many leaves drop off the oak tress you cannot see the surface of the pond! So daily trapping AND removal of leaves is essential for the successful running of the pond.




Two stage skimmer

Moving the water from this first stage into the second stage provides additional leaf trapping and even the pipes feeding the water to the biofilters are slotted 110mm stand pipes, preventing leaves from entering the filters as far as possible.

The Bio Filters

The water is gravity fed in parrallel - to maintian flow rates - to his system using the Happy Koi gULP filters. There 6 chambers or units are placed in two rows i.e. there are three pairs of chamber moving the water in parallel to maintain the necessary gravity fed low rates of his pond which are about once every two hours.



William wanted to use the first stages of the filter to demonstrate, on his own pond, the different ways the filters can be configured. In the first there is a static bed of SuperActiFlo media used as a mechanical filter with a Jacuzzi air blower attached to air bump and backwash the media bed once a week.

The second and third filters are conventional brushes also with the capability to be air bumped with the Jacuzzi air blower when necessary.



All three mechanical stages feed in parallel into moving bed biological filters using the Happy Koi Super ActiFlo media. Water leaving the filters is gravity fed back to a 'pump' chamber through 110mm piping.

This 'pump' chamber is then connected to a return chamber by four 110mm pipes running through the walls which are reduced at the inlet to the pond thus maintain flow rates of the gravity fed system. Two of these pipes are not used - William says they were installed for future changes and experimentation.

The two submersible pumps William uses are connected directly onto two of these 110mm pipes. The pumps are rated at 36kl/hr and 18kl/hr respectively. Water is then pumped from the 'pump' chamber into the 'return' chamber - which is about 500mm above the 'pump' chamber.

In summer William runs both pumps, in winter he runs just the 36 kl/hr pump.




From the pump chamber water is then gravity returned back to the pond via four 63mm pipe returns that return below the surface equidistantly spaced along the back wall of the pond. This creates a gentle circular motion in the whole pond. Excess water flows upwards to a box 500mm above the water, over a spillway or water fall back to the pond.




Oxygenation is further enhanced with air pump sand air stones. UV lights are installed in a stainless steel hood that is suspended above the water in the settlement chamber. This allows the UV globes to operate at full temperature and improves their efficiency by almost 100%.

At is deepest the pond is just over 2m. The pond is well shaded and water clarity is excellent.

There are numerous beautiful high quality koi in Williams pond.