Reference: Unique Koi & More Article Index    Tategoi: The Series    Koi Encyclopedia

Koi Pond Essentials
By Joel Burkard/Pan Intercorp

One of the most common-sense questions that I'm seldom asked is, "What are the essential components of the good koi pond?" But naturally, you asked this question before you put in your first koi pond.

Unfortunately, most folks don't ask the question until after they've already put in their koi pond, or until they've paid someone a hefty sum to put one in for them. It usually ends up being my responsibility to answer the question honestly, even if the customer doesn't want to hear what I'm going to say. Who likes to admit that they've spent four figures (or even five) on something that doesn't work? Expense has a way of dampening the spirits of even the most enthusiastic would-be pond keeper. It's certainly no consolation to realize that the cheapest way to get what you need is to start over.

If you haven't already put in your pond, commit this article to memory before you go to buy your equipment or talk to a pond installer. If you've already put in your pond and you're still not sure if it has everything it's supposed to, you have my deepest sympathies. Read this article carefully. Don't get it too wet from tears or rip it to shreds in anger, you may to need it later for referencing when you've regained your composure.

First things first, before we become submersed in details, I want to issue a disclaimer: The subject of this article is koi ponds and only koi ponds. My experience is only in koi and koi ponds and is based on years of trial and error. I must admit that I have learned a lot more from the error than from the trial. The Japanese say that a koi keeper’s expertise is measured by the number of koi that have perished in his care. If that is true, then I am certainly an expert

If you want a water feature or a water garden, those are something completely different from a koi pond. Frankly, the only thing that I know for sure about water gardens and water features is that no one would ever ask me to write an article about them! I classify a water feature as a landscape design element with water, like a fountain or a bubbler surrounded by stone. A water garden is a shallow pond intended to grow water-loving plants. Neither one is a koi pond, which is, essentially, a life support system or outdoor aquarium for the fancy carp known as Nishikigoi, which we usually call koi.

Before you think that you don't have to read this article because you know you don't want a koi pond, stop and ponder for a moment. What if you change your mind and decide that you want to have koi after you've put in the pond? By then, my friend, it's too late. You can use a koi pond to grow water plants, but more often than not, a water garden is an inadequate environment raise koi.

There are several inherent flaws with water gardens that make it impossible to transform them into koi ponds. Water gardens suffer as koi ponds because they are too shallow and have no bottom drain. They are usually constructed with little or no thought to water flow. They have several features that are sure-fire predator attractants, such as plant shelves that serve as critter perches for heron and raccoon, and shallow areas that heron love to wade in as they fish out your prized koi. Even if you're absolutely certain you won't ever have koi, you're better off building a pond that can serve as either a water garden pond or a koi pond. If you ever want to sell your house, the new buyer might be swayed to the purchase simply because he or she has always wanted a koi pond.

Five Essential Elements of Healthy Koi Ponds

So what exactly do you need to have in a good koi pond? Not much, really. There are five must-haves: bottom drain, surface skimmer, pump, filter, and ultraviolet light. Although it's possible to have a great pond without all of these, it's not easy. Actually, it's harder to go without any one of these components than it is to simply include them all. At the least, build the pond so that the part you're leaving out can be added later when you really need it, as in the case of the ultraviolet light.

Bottom Drain

The purpose of a bottom drain is to remove fish waste and other organic debris that accumulates on the bottom of the pond. Fish waste either floats (which can happen when the fish are not feeling well or not digesting their feed properly) or it falls to the pond floor. The natural force of gravity, coupled with the turbulence caused by the koi swimming in the pond, cause fish feces and other sinking debris to tumble toward the bottom drain. Muck on the pond floor is one of the most dangerous threats to the health of your koi. It's here that many of the most common, and significant, bacteria and viruses will breed and grow. Would you want to go swimming in someone's toilet? Neither do your koi.

It's best to have the pond floor slope slightly to the bottom drain to facilitate the movement of bottom waste toward the drain. Bottom drains are available for both new installations as well as existing ponds that need a retrofit to include a drain. They are inexpensive and worth their weight in gold. The bottom drain also functions as an intake for the pump which will feed the filtration system.


While a bottom drain removes materials from the bottom of the pond, the skimmer takes care of dust and other debris that collects on the pond surface. Dirt and dust particles adhere to the water surface in no matter where you live. As it builds up, it turns to muck. Add to this the grit and leaves that gather on the pond surface, and you have pond scum that is prime territory for pathogens harmful to your fish's health. A skimmer is a low profile, painless way to remove surface debris from the pond before it can become a problem.

There are a number of water garden skimmers available on the market, some of which include filters as well; we prefer skimmers that are skimmers and filters that are filters. The no-niche skimmer is an excellent product that can be retrofitted to an existing pond that doesn't already have a skimmer. We like to use swimming pool skimmers; they're easy to install and service. Prices vary from model to model and from manufacturer to manufacturer.


This essential piece of pond equipment powers both the skimmer and the filter. We recommend an external pump for a koi pond. The biggest reason is safety. All pumps fail eventually, no matter how well made they are. If yours is in the pond when it finally decides to quit working for good, it can do one of two things. If it's an oil filled pump, it can spew oil all over your pond. Even if it is not an oil filled pump, it can release electricity into the pond. Either scenario is bad for your pond and potentially lethal for your fish. As we see it, your koi are worth more than your pump. They're also irreplaceable, while your pump is easily replaced. It makes the most sense, then, to use a pump that has less potential for harming your koi.

The second reason to use an external pump is convenience. A pump sitting outside the pond is easier to service, since you don't have to don your scuba gear or swimming trunks to get to it. You can keep your hands and feet dry while inspecting, repairing, or checking an external pump. External pumps either come equipped with, or are adaptable to, primer pots and leaf baskets that catch small rocks and similar material that would normally clog a submersible pump.

The pump you select needs to be sized to the job it is expected to perform. Boy, there's an understatement! Pump companies publish flow rates that are based on tests done in a laboratory, often without the real-world pond setting that includes lifts, pipes, and elbows, filters etc, all of which will reduce your flow rate. The pump manufacturer might say that the pump gets 2800 gph. But what does that mean to you and me? It means that in a pond situation, with a bottom drain, a skimmer, a lift of about three feet to the water fall, several elbows, a run of tubing that's ten or long, plus the resistance of a filter and an ultraviolet light, the same pump may only get 1400 gph, IF the entire arrangement is designed properly.

In our never ending quest to save money, many in the koi pond industry have gravitated to low amperage pumps, but I'm not among them. In order to move large quantities of water, a low amp pump can often only handle low pressure and lower head (the distance between the water surface and the height to which you are pumping the water). This kind of pump can't feed a waterfall that's 20 feet tall, or pump water efficiently through a tall bead filter. Pump manufacturers realize that consumers pay attention to amperage, and have been known to list the running amperage rather than the start-up amperage. By making the pump appear to be lower amp, they can tell customers what the customers want to hear, not what they need to know.

Finding the right pump is critical and each application is unique. Make sure to size your pump according to its use in the overall scheme of your filter, plumbing, and other equipment. Pumps vary greatly in price. It's best to shop around and ask other koi keepers for suggestions before you make your final choice


Essentially, your pump and filter are like a husband and wife. They need to fit each other well or things will definitely end in divorce. Like the pump, the filter should be sized according to the pond and the anticipated load. Here the load means not only fish load, but also the amount of debris that is likely to enter the pond, whether from leaves, dirt, or the like.

Your fish load should be estimated to take into account the fact that in a healthy environment, your koi will grow like crazy! If you start out with a dozen 6-inch koi, your initial bio load will be a little over one pound of fish. In three years, that load is likely to close to 50 pounds! What if your neighbor needs someplace to keep his koi while he fixes his pond? What if a fellow ponder is moving out of town and gives you his koi? You'll have to have a filter big enough to handle these eventualities.

Filters are like religion; everyone has one and adherents are always convinced that theirs is the best until they find a different one. Like most koi keepers, we've experimented with many filters over the years, and our walkways have the layers to prove it. There's pea gravel from the under-gravel filters that didn't work for our high fish load. There's lava rock that we found totally inadequate for our applications. There's sand from swimming pool filters that got junked once we got tired of changing the sand every week (the same goes for the diatomaceous earth filters). We've tried trickle towers and bio balls, filter mat an. vegetable filters. We’ve even tried Snake Oil and Voodoo but so far, we haven't found the perfect filter. We have found a few, though, that work well for us.

We like multi-chamber filters for koi ponds, based on the filter systems used by Japanese koi breeders. These usually consist of one or more settling chambers and a number of media chambers. When properly designed and maintained, this system can provide consistently high quality water. The only ripple is that they must be periodically cleaned. Unfortunately, no one's yet invented the self-cleaning filter. In the last few years, we've used bead filters successfully as well. When properly sized to the task, they've proven both effective and user-friendly. It's been necessary to clean them more frequently than the chambers in the Japanese-style filter system, but this is less tiresome (and odiferous) thanks to the use of a back wash valve. When used in conjunction with ultraviolet lights, both of these systems are very effective. Ultimately, trial and error will lead you to the precise system that's best for you.

Ultraviolet Lights

The beauty of the ultraviolet (UV) light is that it will virtually eliminate the curse of the pea green water. You can put a filtering system in place first to see if it's enough to keep the pond clear all year. The next year, if you're not satisfied, you can add a UV light if you want additional water clarity.

Although they're sometimes sold as “sterilizers”, they don't really sterilize at the flow rates generally used for ponds. UV lights might sterilize when the water passes through one at the rate of 5 gallons per minute, but in most pond applications, the water is racing past the light at 20 to 70 gallons per minute. At this speed, the light doesn't sterilize. It doesn't need to, anyway. Its primary purpose is to inhibit the growth of free-floating algae and prevent the dreaded pea soup green algae syndrome in the pond. It won’t be effective at sterilizing the water to prevent fish illness or disease. Even if it could, it only neutralizes pathogens that flow past the light, and can't reach pathogens that remain in the pond, on the walls or the pond floor, or on the fish themselves.

Basic Design Considerations


Besides these components, the koi pond should be at least four feet deep and have nearly vertical sides. The four-foot depth doesn't have anything to do with thermal layering and applies no matter where you live, whether that's upper Wisconsin, lower Florida, or along a beach in Hawaii. Koi need a depth of at least three feet to get enough exercise. They need to swim up and down, not simply from side to side in the pond. Large koi like to feed in a perpendicular position, with their mouths sticking out of the water. They can't do that when they're four feet long in three feet of water. You need a pond that's at least two times deeper than the length of your largest koi. For most koi owners, that means a depth of at least four feet.

Water Flow

The right water flow is critical in a koi pond. You don't want any dead spots where debris can build up and never be removed from the pond. A good rule of thumb is to have the water flow in at one end and out at the other. This may not prevent dead spots, but will cut down on them. You can use waterfalls or under-surface returns to bring water back to the pond. If you use a waterfall to create a return flow, make sure to install a bypass in case it leaks or when you need to turn it off in the winter.

If you use an under-surface return, you may need supplemental aeration. Koi have high oxygen demands, especially when they're fed. Many koi owners have air pumps, venturis, or air stones to supply extra oxygen. An aerated bottom drain is also very effective. It has an air bladder (a round disk with lots of holes in it). Air is pumped to the bladder, causing a circulatory effect where air is released at the bottom and raises in a column to the pond surface. The water circulation causes debris to be sucked into the bottom drain. Put aeration devices on a switch so that they can be turned off when you want to see your koi without the distraction of waves or bubbles.

Always make sure to include a few stubbed-off “why in the heck pipes’ through the pond wall. These are extra pipes that you may not need right away. Later on when you wish to make changes to your set-up you'll ask yourself why in the heck you didn't put extra pipes in when the pond was installed.

Budget For It

No matter how you do the math, koi ponds are expensive. If you can't afford one, then make a deep water garden for a few goldfish or koi and in a few years, upgrade to a full-scale koi pond. In the long run, you'll be glad you did. So will your koi, your spouse, and your peace of mind.

A Note on Experts

It's always a good idea to get help from an expert, someone who's truly knowledgeable about koi pond design and installation. Once you find that source, stick with them from beginning to end. After all, if you want to bake a chocolate cake, you get a recipe and then follow it. If it's a good recipe, you'll have a good cake. That won't happen if you cruise the internet, looking for different cake recipes, and then mix them all together to make a chocolate cake, you'll end up with a horrible mess. Make sure your “expert” knows about koi ponds, not just landscaping in general. Ask to see examples of what they've already done so you can be assured that they know what they're talking about. Koi keeping is very popular at the moment, and that kind of notoriety can attract those who talk a good show but can't deliver. When we started our web site ( in 1996, an Internet search using the word “koi” produced fewer than 20 results worldwide. Today the same search produces nearly two million choices. The old saying “buyer beware” is just as true today as it ever was.


  • Previous Article
  • Next Article
  • Series Index


    BACK TO TOPBack to top

    To receive updates on events and specials, enter your email address below and click the 'Join' button. We will not share your information with third parties.


    Home | News | Koi Sales | Koi Reference | Filtration Systems | Hall of Fame | Events | About | Contact

    ©1996-2023 Pan Intercorp - All Rights Reserved. Terms of Use
    18615 80th Ave NE, Kenmore, WA 98028 USA
    Phone: (800) 827-5819   |   E-mail: