A Guide to Modern Koi Pond Construction

Deep water returns

[Mid water returns] In the late 80's several people installed a mid water return. This was usually situated about three feet below the water surface, and the main idea was that it would move the water and so force the fish to swim against the current the same as they would in their natural environment. The main problem was that it required a high pressure pump, such as a swimming pool pump, to ensure that it does work correctly, and few members found it very successful. In cases where it is still in use then it is usually powered by a separate pump probably from the skimmer, and 1½" pipework is usually used. Fig 14a shows a typical layout for this type of return.
[Deep water return] A system that is now being used in several big ponds in the North may well be worth considering, is a deep water return. Fig 14b shows a sketch of this, and a plan view is shown below in fig 14c. The pipe work is fitted quite low in the wall of the pond, and is set at an angle of about 45 degrees in both directions. The idea is that the flow of water is directed towards the base, and also at the same time causes a swirling movement so that any debris will be directed towards the bottom drains and so it is removed to the vortex chamber.
With a large pond you will require several of these.

[Deep water return - plan view]

Again there is the problem of the flow and also the size of the pump and a swimming pool pump may be required instead of a smaller circulating pump. One of the well known 16,000 gallon ponds in the North has several of these deep water returns fitted and the system appears to work very well. In this case each of the deep water returns is powered by a Sequence ¼ hp which has surprised several koi keepers as these pumps are not pressure pumps. These Sequence pumps do require 2" pipework to be efficient.
Deep water return before cutting Deep water return being trimmed
The first photo shows the pipe before it is trimmed, and the photo on the right shows the finishing of the pipe before final coat of fibreglass. Check this page for more details on this work.
 

Since 2003 these deep water returns are now becoming quite popular with koi-keepers building a new pond.

Main reasons for deep water returns / TPRs :-

  • Extra current to ensure no dead spots/ efficient mixing (especiallyimportant for larger ponds greater than say 6000 gals).
  • Current for the fish to exercise against.
  • Additional aeration and gas exchange.
  • Current to sweep Koi waste more effectively to the drains.
Fibreglassed pond showing deep water return

There are some people these days who do not consider it necessary to put the deep water returns in at an angle.
In this photo you can see the deep water return is at right angles to the wall. On a pond of some 5,000 gallons then another one would be probably be placed on the opposite wall, but on the other side.
This method of doing it is much easier when fibreglassing, and also easier to place within the wall.

TIP. If the pond is not heated then the deep water returns should be shut off in the winter so that the fish can rest on the bottom.

 
There has been some concern that with this movement of the water in one direction that large show fish can build up more weight on one side of their bodies. To overcome this some koi keepers with large ponds have put in an extra set of these deep water returns facing the other way. They then fit changeover valves and so can have the water circulating clockwise one week and anti-clockwise the following week. This is not considered necessary for most ponds.
 

Next we will look at benching the base.

This page updated December 2004

This website started with a booklet which I made up originally for the help of those members of the BKKS - South Wales Section who were intending to start building a koi pond, and as the website has expanded more information and articles from other people have been included. This is for general guidance only, and we do not take any responsibility for problems that might occur by following these ideas. It is important that you check out everything in your area, and check on local laws and rules that may apply.
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