Filtration System for my Third Pond

My current pond consists of a main Koi pond, a water feature that overflows into the Koi pond and a physically separated garden pond that shares the same filtration system. The drawing below describes the filtration system and I would recommend this as a minimum design to anyone who is thinking of building a new Koi pond. This design overcomes a few problems that I encountered with the earlier filtration systems used for my first two ponds.

The drawing below shows the plan view of the filter.

The first chamber is the gravity pipe chamber or settlement chamber. Water enters the settlement chamber at the bottom from the pond's bottom drains through two 4 inch diameter (100 mm diameter) pipes. Two other lead-in pipes (75 mm diameter) pull water from my water garden pond and also from the bottom drain of my water feature. There is also a small skimmer pipe (75 mm diameter) that removes surface debris from the Koi pond to the filter. The settlement chamber allows for solid waste to settle before going into the filter media.

Each inlet pipe in this chamber is configured with a socket to allow me to push in standpipes to stop water flowing into the filter during filter maintenance. Photo above shows two standpipes in position.

A copper pipe with a tap allows easy refills from the water mains without the need to pull a garden hose. It comes with a float valve (commonly used in cistern) that automatically shuts off the tap water flow when the desired water level is reached. This chamber also contains a 50 mm diameter overflow pipe that leads to a drain.

Filtration Chamber 1 is for mechanical filtration. It contains filter brushes which acts as the mechanical filter. The brushes trap solid wastes and debris like fallen leaves. This can then be removed and hosed down when needed.

Filtration Chamber 2 is for biological filtration. It contains filter mats, placed vertically and supported by plastic grating at the bottom. The mats provide the areas for the bacteria to grow.

Filtration Chamber 3 and 4 is for biological filtration. It contains sacks of crushed cockle shells and coral chips, supported by plastic grating at the bottom of the filter chambers. The shells and coral chips provide the pH buffer needed to control the pH level in the pond. It also provides the areas for the bacteria needed in biological filtration to grow.

The Return Pump Chamber contains two return pumps. The pumps pushed the filtered water back to the Koi pond and water garden. One return pipe goes to my water feature and water garden. The other pushes water out through 3 venturi pipes into my Koi pond. The water feature and venturi pipes provide aeration for the pond. Once water is pushed out from the Return Pump chamber, gravity will draw water from the pond's bottom drains into the first chamber.

Each filter chamber has a bottom drain that leads to the Sludge Chamber through a 40 mm diameter pipe. Ball valves are used to open and close the bottom drains.

A long PVC pipe, with tailored ends as shown, allows the valves to be operated easily from above and makes filter maintenance easy. I can flush the bottom of all my filter chambers, especially the settlement chamber, within a few minutes. This makes the task so easy that I can do this almost daily.

The filter shell is made of thick reinforced concrete, as is the rest of my pond. Pre-casted, one-inch thick concrete slabs are used to construct the filter chambers. Balau wood is used for the removable covers.