How to Plumb a Koi Pond

Designing and plumbing a koi pond requires careful thought and planning from both plumber and owner

How to Plumb a Koi Pond

The best koi pond designers use a wide-diameter pipe, like 4-inch or larger, with no angle fittings. If corners need to be made, they should be 90-degree sweeps or flex pipe. (Photos by James Careless)

At first glance, plumbing a koi pond — a backyard body of water stocked with colorful fish — looks simple. You connect the pond, bottom drain(s), skimmer and filters together using pipes and pumps into a continuous closed loop system — just as you would a swimming pool.

Except, this isn’t a swimming pool: The need to gravity-feed water from the pond to its mechanical and biological (beneficial bacteria) filters, and then return it to the pond, requires an approach to piping that minimizes friction at all costs. This is why the best koi pond designers use wide-diameter (4-inch or larger) PVC pipes with no angle fittings, and when they need to turn corners, they use 90-degree sweeps or flex pipe.

The science behind designing a low-maintenance, reliably healthy koi pond is enough to fill a book, and much more information than a plumber needs to know. There are many different pond configurations out there, and there are many ways to filter the environment. But as long as the client or contractor has taken the time to select the pumps, filters and other equipment properly as part of an overall pond design — or hired a competent koi expert to do the job for them — all the plumber needs to know is how to connect everything to maximize water flow while minimizing friction.

That said, “I’m not going to lie: It is truly apples and oranges,” says Joseph McAuley, a highly skilled, creative journeyman plumber in Ottawa, Canada. He was the one called to fix the plumbing disaster documented below. “In a house where you’re doing plumbing, you deal with toilets, sinks and bathtubs and they all work under the same principle. But a pond is completely different. It’s still plumbing, but it’s like comparing city plumbing to rural plumbing. It’s not the same thing.”

What not to do

The initial plumbing job in the koi pond (done by the general contractor who built the pond’s concrete container) is a prime example of how not to plumb a koi pond. It was full of errors that drastically reduced the flow of water from the bottom drains to the filters. In a pond, filters remove debris and toxins from the water.

Even though koi ponds use pumps to move the water around, it is imperative to have an efficient gravity-fed system for the filtration process to work.

“This is why you want to create the most streamlined plumbing installation possible, while using the least amount of fittings,” says Zac Penn, owner of Deepwater Koi Innovations. “You also want to use sweep fittings wherever possible to reduce the friction loss, while using large-diameter pipes is a must because koi ponds need to have the filtration running 24/7 to keep healthy water.” That’s important; pools don’t run 24/7, but ponds do.

McAuley followed all of these principles when he replumbed the koi pond, using minimal fittings and sweeps to maximize water flow. The result: The water management system of this 9,500-gallon koi pond has been working flawlessly for two years, with sufficient gravity-fed flow to keep all of the filters and pumps running optimally.

The three keys

No. 1 — Select the right pipe

In some cases, the client may leave it to the plumber to decide what type and size of pipe to use for their koi pond. If they do, be sure to choose PVC over ABS. PVC is stronger and more robust than ABS, which allows it to survive changing weather/temperatures above ground and weight/pressure changes from the soil when buried underground.

“Rigid Schedule 40 PVC pipe is the best option available for koi pond plumbing,” Penn says. “The inside wall of the pipe is smooth for less friction, and the inside diameter of Schedule 40 pipe is the same as what the pipe is labeled.”

As for deciding how to best lay the pipe and what diameter(s) to use?

“Most fitting manufacturers give you a coefficient of drags with respect to their products, which you can use to calculate flow rates,” says Mike Swanson, owner of Koi Acres. “You use this data to do the math by factoring in the pond size by gallon and a desired turnover rate, namely how many gallons per hour that you want to move through the filters to keep the water healthy.”

The recommended turnover rate is usually once/hour if your fish load is one fish/500 gallons.

No. 2: Remember head pressure

Unlike a house where water flows from top to bottom, water in a pond goes sideways. Filters are installed at or below the water level, and sometimes above. When water has to move up, it creates head pressure that impedes the water flow, which has to be overcome by using pumps with sufficient gallons per hour capacity.

“For example, a 5-foot-high waterfall will add 5 feet of static head pressure,” says Clayton Arnall, owner of Everything Ponds. “A pressurized filter might add 5 to 10 feet of head depending on how dirty the filter is. The pipe will also add pressure, which is why it’s important to use the right size pipe.”

Fortunately, Everything Koi has created an online tool to calculate head pressure in a pumped system, as well as the water speed in the pipe. It can be found at

No. 3: Unions are a must

When a house is plumbed, the connections are done and that’s it, so gluing them in place isn’t a problem. But a koi pond is different: PVC pipe unions are a must for every equipment connection. The reason?

“If we need to replace a pump, valve, or filter, we can unscrew the union and put a new one in place,” say Eric Triplett and Leslie Triplett, owners of The Pond Digger.

Final words of advice

For those plumbers willing to take the plunge, koi ponds can be an interesting and profitable venture, as long as they heed the following advice.

“Check your ego, be open-minded to the uniqueness of koi pond filtration and don’t fly from the seat of your pants,” Penn says. “And if you notice that something in the plans doesn’t look right, then talk to the designer. If a change needs to be made, the pond designer should also be humble and admit that they didn’t have the best idea originally.”

At the same time, “keep it simple,” McAuley says. “Otherwise, the friction loss created by all the extra fittings you put in won’t allow the filters to work properly.”


Comments on this site are submitted by users and are not endorsed by nor do they reflect the views or opinions of COLE Publishing, Inc. Comments are moderated before being posted.