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I would like to thankEric Poingdestre ofKoi Cymru(South Wales BKKS section) for all the help and advice during the construction of this pond.
Before any work was carried out many hours were spent on the planning stage.Due to the proximity of a sewerage pipe it was decided that the pond bottom would be sloped. To what depth, at that stage, was unknown. It was also decided that due to the heavy slope then only one bottom drain would be required.(Thought was also given at this stage to pump flow rates and with only one bottom drain the flow rate through this pipework would be twice that of a similar system with two bottom drains for the same planned flow rate.)Hence a reduced chance of any settling out in the bottom drain pipework.
Excavation work started in march 1997 and it took five men 3 weeks to completely remove 10 large skips of earth.Unfortunately, we were unable to get permission to remove our back fence so that we could get in with a mechanical digger. All of this was removed by hand and the transported around to the front of the house,up the drive and then into the skips.Although the digging was fairly straight forward (The earth was soft due to the rainfall ie march) it became more difficult the deeper we got! It was neccesary to rig up a ramp and a platform half way down to place the wheelbarrows for digging at lower depths.A depth of 5 ft sloping down to 7 ft was achieved.After the concrete base and benching was carried out,this would give a final depth of 4 ft sloping to 6ft 2 inches.
After digging was complete it was then necessary to position the pipework.An extra lenth was left on to give twice the hieght.This was for testing purposes only.(the bottom drain end was blanked off and the pipework filled with water to twice the pressure head and left overnight to check for leaks).
Prior to laying of the concrete base wire reinforcing was layed down and pegged to keep it approximately 3 inches of the ground.The first batch of ready mixed concrete to be delivered was approximately 4 metres cubed which when delivered nearly engulfed the garden hut.Laying of the pond bottom was carried out in one go which worked out at an approximate depth of 8 inches. Some places where the concrete was even 1 ft deep,this was due to the uneveness of the excavation.
The bottom drain and the associated pipework was completely encased in concrete and this was carried out in one go. It was neccesary to stake down the bottom drain and associated pipework to prevent them from lifting and to keep them level.The level of concrete around the bottom drain was around 1 inch below the neck to allow for benching and rendering.This just about covered the pipework in the first go.
The blocks used for constructing the walls were 18x12x6 inches thick.A gap of 3 inches was left between the outside of the blocks and the excavation wall and was gradually back filled with concrete to give a wall thickness of 9 inches.The blocks which formed the circumference of the semicircle were cut in half for a more gradual radius and stronger joints.
Preperation for drainage of vortex chambers to sewerage waste was carried out by placing the filter unit in position and then fitting the pipework.
Preparation of all inlet and outlet pipework was carried out by covering the pipework with solvent weld cement and then covering this area in sand whilst the solvent weld was still wet.This was carried out in the area where the pipework penetrated the pond walls.The bottom drain and skimmer unit were prepared in the same way as the other pipework as can be seen from one of the above photographs.
Prior to rendering and sloping of the pond bottom,it was necessary to make the corners into curves ( to help water flow and reduce the possibilty of any dead areas).Rendering was carried out all in one go and fibromix was added to the sand and cement to manufacturers reccomendations.Unfortunately I have not got any photographs of either benching or rendering procedures.
Whilst waiting for the rendering to dry, which took almost 2 months due to one of the wettest summers I could remember,the finishing off of the pipework and fitting of the sand filter was carried out.Choosing the correct sandfilter for the system was easy.However it was quite difficult in choosing the correct flowrate for the pump which supplies the sand filter.Although only 2500 galls per hour was required a greater capacity pump would be required to drive the water through the sand filter.A pump of a capacity of 4500 gallons per hour was used at first but upon starting this pump it just emptied the filter chambers.A smaller pump of 3500 gall/hr was then tried and gave the approximate flow rate of 2500 ie correct flowrate for the sand filter,cloverleaf filter and the pond ie turnover of every 2 hours.
Once the rendering was dry then 4 coats of G4 was applied, also carried out as per manufacturers instructions.2 coats of clear followed by 2 coats of black was applied and the easiest way to carry this out was with the use of a tressel (I hope to submit a drawing of this at a later date).Apart from the first coat, each coat was apllied whilst the previous coat was still sticky.This took only 20 miniutes between coats due to the sunny weather.
Once the G4 was allowed to cure, (4 Days)the pond surface was washed down with clean water and then this water was pumped out.Water was then added via a water meter and a purifier consisting of a pre-filter and activated carbon.Once the pond was full the pumps etc were all run for a few days to check for leaks etc.Once it was proved that the water level was maintained the fish were gradually added to the pond.Although the fish were added fairly quickly ie within a few days,this was only possible as some of the media which was in the filter system for the tank which temporarily housed the fish whilst the pond was being built(kept in the garage).Once all of the fish had been transferred then the old filter was placed between the skimmer and the return to the pond.(Waterfall and Vegetable filter were constructed at a later date).This kept Ammonia and Nitrites to an acceptable level until the bacteria had colonised in the main filters ie other than slight fluctuating of the waters p.H I did not have any problems with the so called "New Pond Syndrome".