Solving the Filtration Challenges of a Dining Room Koi Pond

Published on October 30, 2024

Dining room koi pond
Non-slip glass panels on the floor lead to a glass enclosure around the tree.

When my phone rang in May 2023, the caller ID showed Yountville, California. When I first saw the number, I laughed to myself, because my wife Janon and I have been to Thomas Keller’s French Laundry restaurant several times. My first thought was, jokingly, they were calling to confirm a reservation!

I regularly have obnoxious responses to cold sales calls just for sport, and this was no different. “Hi, I assume this is the French Laundry and you’re calling to confirm our upcoming reservation?” popped out of my mouth. That was followed by a pause on the other end and then a man’s voice saying, “Well, no, I was calling to possibly hire you.”

We both laughed, then he introduced himself as John Wargo of Wargo Construction. He was working on a project in Calistoga that included a koi pond. 

Welcome Home

Floor frame installation

The project was a complete remodel of a 150-year-old bed and breakfast in Calistoga, originally called the Pink Mansion. Its new name would be Okaeri, which is a shortened version of the Japanese okaeri nasai, which means, “welcome home.” Okaeri is what you say when you leave or come home. It’s one of the common expressions for saying goodbye or welcome.

There was an existing 10,000-gallon indoor swimming pool the owners wanted to convert into a koi pond. Built under the dining room floor, the pond is viewable through glass panels randomly installed throughout the floor. A 10-by-10-foot open section in the center of the floor is surrounded by a glass panel railing with a large potted tree. John had been working on the suspended floor frame and now needed help with filtration.

I flew down to look at the scope of the project and quickly realized there was no room for filtration. Not anywhere above water level or outside the building. The outside of the pool shell was exposed underground with limited area to work in.

There was a space of 6 or 7 feet between the pool shell and the outside walls surrounding it. This space was half underground and half exposed to the front under the main floor. This meant we could build something that surrounded the structure with the only issue being it was below water level.

Filtration Integration

Drawings depict the overall system (top) and inside
wall (bottom) with the overflow regulators.

The pond was designed as a still pond or reflecting pool. This meant I needed to oxygenate the water outside the pond and return oxygenated water to the pond. I decided to use overflow regulators from the bottom drains in a similar concept I had used before. Three LWS vertical pond return drains would flow to the corners of the deep end wall and then up to the regulators. The overflow regulators would establish the pond level while allowing the full volume of the pumps to remove water from the bottom, flowing down to the prefiltration chamber in what would become the filter room.

The skimmer would be a standpipe at the same level as the overflow regulators. It would flow down to a suspended basket in the prefilter. The three overflow regulators and the skimmer standpipe assembly would be encased in concrete at the end of the pond, keeping the pond water surface separated from the units.

The filtration system would be an old-school chamber design mixed with some new inspiration. The bottom drains flow into the left end of the prefilter chamber and are directed up with standpipes as in a radial separator. A divider plate directs the water downward at a slower rate toward the bottom of the tank, where it travels across the chamber and over another divider plate with a weir flap at the top. This mimics the path of a radial separator. It allows only the cleanest water removed of heavy solids to flow over the weir into the prefilter media chamber.

Prefilter Details

The prefilter media consists of Matala cubes that float at the top of the chamber. The pond water flows down through the media, passing through a divider plate and out two 6-inch lines around the corner into the aerated media biofilter. The settlement chamber and the prefilter chamber each have bottom drains leading to a discharge manifold. The pre-filter has an air-blower cleaning manifold and upper rinse drain for cleaning the media. The B-37 skimmer basket is mounted on the 4-inch pipe coming through the wall above the settlement chamber, with the basket partially suspended in the water. I molded a slide assembly with a locating pin to easily remove the basket for cleaning.

Around the corner from the prefilter chamber, I placed a concrete platform over the two 6-inch transfer pipes for the three W. Lim Wave 1 pumps. This allows for easy access and maintenance.

The aerated biofilter chamber is filled with Matala cubes, as was the prefilter. The 6-inch lines flow water up into the center of the chamber and out through two custom-built, 6-inch stainless-steel outlet screens. This prevents the media from flowing back into the lines. The media is aerated with two 120-lpm Medo air pumps and aeration tubing manifolds mounted to the divider plate.

The three W. Lim pumps pull water from below the divider plate with two of them pumping to a manifold assembly connected to the three vertical pond return drains. The third pump sends water through one of my 86-watt UV lights and a manifold connected to the four 2-inch returns at the far end of the pond. This creates a directional pond flow from the shallow end to the deeper end, with the vertical pond returns creating a toroidal circulation in the deeper end above the bottom drains.

Three 45-lpm Medo air pumps supply the aeration rings on the VPR drains and are set with a timer to come on twice a day. All five pumps, two Medo 120s and three Medo 45s, are mounted on a shelf connected to the end of the prefilter chamber above the pond pumps.

The completed system is compact and easy to access, just inside the entrance door to the filter chamber area.

Drains (left) are installed in first chamber. A weir plate (center) is placed next to the prefilter chamber. A skimmer basket (right) is suspended in the settlement chamber.

Final touches

Paul Parszik of Artisan Aquatics drove up to apply the polyurea coating and did an amazing job. The interior walls and floor of the filter chambers were coated as well.

I arrived for the second time in September 2024 to check over the system and help get it running. I was pleasantly surprised at how accurately every detail was constructed. Randy Willems of Paradise Pools handled all the major plumbing, drain placement and concrete work, doing an amazing job. He took my 3D SketchUp drawings and brought them to life perfectly.

Final test

Aerated chamber with media.

The final test was turning everything off to observe the water level in the filter chambers when the power goes down or the system is shut off for maintenance. The water rose about 4 inches and stopped. This is the volume of water in the pond above the overflow regulators and skimmer standpipe. When the pumps come back on, everything self-adjusts and works as normal.

Once everything was running, the final piece was the autofill. It’s mounted on the left end of the prefilter chamber, just above the bottom drain inlets where the water is closest to pond level.

One interesting note about this project is that there was no edge treatment or aesthetics to deal with. The visual impact of the pond is largely the dining room it’s situated in. The design was the work of Meredith Rebolledo of Meredith Rebolledo Interior Design. She did an amazing job of incorporating koi and lily pad fabric in the backs of the bench seating and the curtains in the dining room. White ceramic planters placed along the wall above a mirrored insert over the seat backs soften the wall and make the room appear larger.

I always enjoy working with a group of people with a vision and the ability to carry out the design. Even when my participation is largely invisible.

To read about more indoor koi ponds from Kent Wallace click here.

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