|Before you start digging your new koi pond you will need to consider a few basic variables. First, Do you want a proper koi pond or do you want a water garden? They are not the same thing. A water garden is usually shallow with lots of plants and very few fish, usually just a few goldfish. A koi pond will be much deeper, bigger and you will need to provide much better filtration and water quality. The purpose of this section we will discuss the design of a proper koi pond. Can you keep koi in a water garden design? Yes. Will the koi flourish and develop as well as they would in a well designed koi pond? maybe, but it will require a lot more work in the form of weekly cleaning and maintenance. The real beauty of a well designed koi pond is the low amount a work it will require to keep very high quality water.
When designing the the pond you need to first choose your location. Under large trees is not ideal since the falling leaves will be a constant problem. Also you will need to dig through dense roots. A spot that has partial shade and no runnoff from nearby sprinklers is ideal. Koi prefer the shade, but they do require some sunlight to maintian good health.
Once the location is decided you then need to then determine depth. Koi prefer at least 3 to 4 feet, but 6 or even 8 foot koi ponds are not uncommon. The deeper you go the better the koi will develop, the more stable the water temps will be and the more gallons you can have with a smaller footprint. With proper stocking density and filtration, you should be able to see all the way to the bottom of an 8' koi pond.
Once you have decided on the depth you need to consider quality of materials and budget. The most economical will be a EPDM liner pond. These are sturdy and easy to install, but they also create folds which allow for debris to get trapped and decay. The other end of the spectrum is a cement pond made from either cinder block or sprayed concrete. These are then sealed with a variety of products available that can be applied by the very brave do-it-yourselfer or a professional.
When you have the general lay out, placement and style of the koi pond we can start to focus on some of the basic elements that go into a proper koi pond. You need to consider the overall dynamics and flow when designing the pond. You don't want any areas with poor circulation. It is best to bowl the bottom and round the corners so the waste is not trapped and it will naturally flow downward towards the bottom drain.
A bottom drain is the single most important aspect of a proper koi pond. There is absolutely no substitute for a bottom drain. It will make the cleaning and maintenance far easier and without a bottom drain providing high quality water for your koi will be very difficult if not impossible. A retrofit bottom drain can be installed for those who already have their pond built, but it is not as effective as a properly installed bottom drain. Many fear cutting the liner, however the drains are easy to install and do not leak when installed correctly. Ponds that rely solely on a skimmer will not be able to remove all the sinking waste produced by the koi. The waste will remain in the pond causing a whole host of heath problems ranging from premature aging and loss of color to infections and death. The bottom drain allows the vast majority of the solid waste to be easily and effectively removed and sent to the filtration system.
That brings us to the next aspect of the koi pond design, the filter. There are two types of filtration, mechanical and biological. Both are equally important. The mechanical filtration must come before the biological in the overall design. This way the solid waste will be removed before it reaches the bio filter. When the solid waste is allowed to enter the bio filter it will quickly clog the media and kill off all your bacterium. There are many types of mechanical and bio filters on the market in all sorts of price ranges. One thing to keep in mind when choosing a filter system is your overall goals with the pond. If you want large show quality koi then you will need a high quality filtration system to provide superior water quality. If you are happy with just some nice looking koi and you are not concerned with body conformation and color development, then you can use something a bit less sophisticated. In fact many basic filter systems can be built in one weekend by the average do-it-yourself hobbyist and they are more then adequate for most koi ponds.
Some hobbiests who want very clear water will install a UV filter. The UV will help prevent the dreaded "green water" otherwise known as algae blooms. A UV filter is a valuable tool in koi pond filtration and should be considered if the budget allows. Keep in mind though that green water is not the enemy. In fact the koi will thrive in green water. But that doesn't do a lot of good if you can't see them...so the choice is yours.
After the filter you have the water return. Most will opt for a waterfall of some sort. These can be very pleasing to look at and listen too. They will also help aerate the water. But a waterfall is not the only option. Many times those with larger ponds will install TPR's, or small underwater jets that will aid in the ponds circulation. Another option is a spray bar. This is a high-powered jet that sprays the water over the surface of the koi pond. This will aerate the water much better then a waterfall and it will also help to remove nitrates from the water. And don't be afraid to use all three of the above elements at the same time for superior circulation and aeration.