It's all about filtration. A proper filter system is the key to a successful koi pond. Many factors must be considered when designing a filter system. All components must be coordinated to ensure proper function. The following components must be carefully planned before you even start digging:
- Pond gallons
- Pond shape
- Pipe sizes and configuration
- Filter components
- Pump flow rate
- Total Head Pressure
- Proper circulation
- UV Clarifier size
- Backwashing of waste
- Fresh water and overflow water
SELF CLEANING POND SHAPES
Design your pond with straight walls and a sloping bottom. The vertical walls will not collect debris and they will also help keep predators out of the pond. Ideal water depth for a koi pond is 3 to 4 feet. The bottom should slope to centralized bottom drains. These drains will take the dirty water to your filter. Cement ponds can be vertical. Liner ponds may need an angled wall in order to prevent the soil from caving in. The liner wall can be a vertical wall for the first 18 to 24 inches depeding on the stability of your soil. The wall can then angle towards the floor to make up the additional depth needed to achieve 3 to 4 feet. If you want aquatic plants you may add planter shelves in various artistic locations. Make the shelves at least 18 inches wide so the plant pots will be stable. The shelves need to be about 12 inches deep for bog type plants. This will put about 2 to 4 inches of water above the pot. Lilies need to be in 18 to 24 inches of water.
Remember however, that an 18" or less plant shelf will also be a place where predators like racoons and herons can stand. So keep these shallow shelves to minimum areas whereby if a predator does stand on it he cannot walk around the entire perimeter of the pond. Put these shelves in limited areas that will compliment the look of the pond but not create a walking zone for predators.
The diagrams below give some examples.
The diagram below shows a top view of different shapes that can be considered self cleaning. Notice the placement of the jets. The jets are positioned to flow the water along the perimeter of the pond walls. The jets do not point out to the middle like a swimming pool. The jets flow follows the contour of the pond walls and creates a toilet bowl effect funneling debris to the center drains.
The diagram below shows the installation of a liner bottom drain. The drain leads to your filter system. They should be placed at the deepest point in the bottom of the pond. There are many brands of bottom drain for rubber liners. They usually have a large flange and one or two gaskets. The rubber liner is place between the two halves. Use silicone glue or polyurethane adhesive caulking found in your hardware store on both halves and then use screws to tighten everything together.
Use 2" drains and 2" pipe only for systems that feed directly to your pump. Ponds larger than 4000 gallons with pump first systems may require 2.5" or 3" drain and pipe size to accomadate higher flow rates and greater debris. If you are using a gravity flow directly to your filter like a settling tank or sieve then you will need to use 3" or 4" bottom drains and plumbing to accomadate the flow to these types of filters. Notice that the pipe is buried in a trench line beneath the liner so as not to interfere with bottom shape.
The diagram below shows the installation of a cement bottom drain. Notice that the drain pipe is positioned straight through the concrete. The horizontal pipe leading to the filter system is buried in a trench below the conctrete so as not to reduce the strength of the concrete. The drain cover is merely a large grid which is embedded in the concrete and set flush with the bottom. Notice that the shape of the concrete and the rebar is formed into a bowl. The grid is positioned above the drain pipe by 3" to 5" to spread out the flow better. We like this type of grid because it keeps baby fish and large leaves out of the pipe. Some hobbyists prefer to use an anti-vortex bottom drain which helps to draw water from the sides. This is fine if you have a light leaf load from surrounding trees. A heavy leaf load will jam up your pipe with the anti-vortex type drain. Remember that baby koi can get sucked into an anti-vortex type drain. The grid type of drain, in our experience draws water very nicely and does not have some of the drawbacks of the anti-vortex type.