What filtration to use?
This is the single most important decision you will be making in the conversion process of making your swimming pool a suitable location for the housing of a collection of Koi fish. Our opinion has always been the same - buy the best possible filtration that you can afford and always overdo it.
When it comes to Koi ponds you can never, ever overdo the big three: Filtration, Aeration and UV. So put plenty in - if you don't use it it will never be wasted on a Koi pond.
You also need to think of the picture as to what the Koi pond is going to be like in ten years time. At this stage hopefully you will have a number of sizeable Koi swimming around and it is when your Koi are large that they place the most load on your filter system - the slightest shortcoming in your filtration can translate into catastrophic consequences.
In other words it is important to plan for the future. Once your filtration is in place it can be more difficult to add to it later on.
As mentioned previously ensure that you give yourself enough space for your filtration to be able to easily access it for maintenance in the future. You will spend considerably more time with your Koi pond filtration than you will on your old swimming pool filtration so make it as easy as possible to do. If you plan appropriately you can make your filtration maintenance very easy and quick to do.
The most important thing to understand is that filtration on your Koi pond is going to be significantly larger and slightly more complex that the filtration you have currently on your swimming pool. In most cases you will need four to five times the space you have currently allocated to your filtration, and in some cases if you go extreme in your filtration we have seen systems that occupy more surface area than the pond itself.
A rough rule of thumb is to allocate one third of the surface area of your pond for filtration. In other words if your existing swimming pool is 8 x 4m, or 32 square meters you should allow for about 10 square meters for your filtration. This will give you plenty of space to move in the filter area, and to install all your equipment without it all piled up on top of each other. Personally we prefer having space that isn't being used to not having space available to fit, say a protein skimmer, or some other piece of kit later on in the future.
In most cases swimming pools do not have bottom drains like Koi ponds do. This is the most significant obstacle in converting a swimming pool into a Koi pond as the issue of removing debris that settles on the bottom of the pond becomes the problem.
There are only really two ways of addressing this. The easiest is to simply use an appropriate submersible pump located at the deepest point of the pond. Another option is to use a pipe located at the deepest point with slots cut in it to suck up the debris.
A third but seldom used alone option is to agitate the debris by using air stones located on the bottom of the pond at the deepest point. By blowing air bubbles at the deepest point the debris is stirred up into the main body of water where it is then carried off to the pump and taken out by the filtration system.
Using air to create turbulence to keep dead areas of debris accumulation from forming is often used in conjunction with either the slotted pipe route or the submersible pump option. Air stones have the advantage that they can be easily moved from one location to another. And of course the added benefit of the massive aeration that airstones offer to the pond (by creating vertical circulation of the pond water) cannot be overstated.
Larger debris such as big leaves that have sunk will need to be removed manually by means of a net.