Koi pond with rock border

You’ve fallen in love with koi fish. You’ve looked at some koi ponds. You’ve made the decision that you want to build a koi pond of your own. That is the easy part.

Now for the fun part. Actually building it.

Even if you’ve done all your research about being a koi keeper and feel ready for the job, there are a few things that you need to know before you start breaking ground on your first pond. In some cases, these tips apply for above-ground builds, too.

Call Before You Dig

Digging a koi pond is not just a tough job, it can be a dangerous one, too.

There are more than a few hobbyists that have put shovels into the dirt only to cut a buried pipe or utility cable. If you are using an earth mover, it can be even easier to chop through a gas or electric line.

This can be a costly endeavor, as well as a potentially harmful one.

So, before you start, do a little digging (online, not in the backyard). Call your local municipality to confirm that the area for your new pond is clear of any potential hazards. If there are any, the utility company will mark or stake them.

Shape

Diagram of ideal koi pond shape for ideal water flow
courtesy: ebuildapond

The shape of your koi pond might seem like a question of type or personal taste. And it is. It needs to be something that is pleasing to your own aesthetics.

But for koi ponds, shape can affect waste build up, ease of maintenance and the desired volume of the pond.

Some pond shapes, especially complex shapes, will break up or slow down the water circulation. This creates “dead” areas in the pond that collect dirt, debris, and waste.

This waste accumulation can affect water parameters. Unfiltered, excessive waste or decomposing organics will add ammonia and nitrites, which are hazardous to koi.

Perhaps as important as shape are the koi pond’s contours. If you are determined to have visible corners in your pond, consider rounding the bottom to help the water circulate waste closer to its intended destination.

The same goes for the contours from the sides to the center (or wherever waste is intended to accumulate for automatic or manual removal). Sloping to this area makes cleaning much smoother and helps with better water parameters.

Also, if your pond is in a climate where freezing occurs during winter, sloped sides will push ice upwards instead of against the pond liner. This helps to place less stress on the liner.

It is always a good idea to mark the shape of your pond out well ahead of time. String, a garden hose or landscape paint are all options. Let it sit for a while and let it sink in. Seeing that same shape a few days later might make you rethink what you want it to look like.

Depth

Koi keepers will offer a number of differing opinions on the optimum depth of a koi pond. Some claim the minimum depth should be 2ft. Others say 3ft. Maximum depth should be 4-5ft deep. Or is it 6ft?

You want to give your koi the best possible chance at a good home, but you will also want to be able to see them.

A view of koi pond depthThere are lot of considerations when it comes to how deep to dig your koi pond.

  • Climate: in the summer months, deeper ponds will heat less slowly, making the temperature more consistent throughout the day. In winter, a deeper pond is less likely to freeze all the way through.
  • Predation: the types of natural predators in your area can determine how deep you should have your pond. Deeper ponds make it harder for non-aquatic predators (like raccoons and cats) to find and hunt your koi fish.
  • Number of fish: the deeper your pond, the higher the volume of available space. More gallons mean a greater number of fish can live happily and comfortably.

Number of Koi Fish

Most koi kichi will tell you that buying koi is like eating Pringles—you can’t ever have just one.

Sanke, Showa, Kohaku, standard or butterfly, doitsu or scaled. With 38 varieties of koi available, you can fall in love with many different types of koi throughout your life. And you will.

So before you build your koi pond, you have to be 100% honest with yourself. How many koi do you expect to get? Once you have that number, add 100 gallons to your dig. You will get more.

The number of fish (or fish load) you have determines the size that you will need to make your pond. The accepted rule of thumb is 1” of fish per 10 gallons of water. Under the right circumstances, koi can grow to be longer than 24”. These bigger koi require room to maneuver.

Access to Power

If you are planning on running pumps, UV filters or anything that requires current, you will need to factor that into the location of your pond. If you are using an outlet versus a dedicated breaker, it will have to be within the reach of whatever length cord you have at your disposal.

Also, make sure that it is a GFCI outlet.

Shelves built into a koi pondShelves

Pond shelves are more than just for aesthetics. If you plan on having aquatic plants, you need to know the optimum depths for them to thrive.

However, if you have predators in your area, remember that shelves offer them a convenient vantage point from which to fish. So, plan shelves carefully.

Tree Roots

Natural shade can be a great way to help regulate water temperature If you are looking to use the natural shade of trees to help regulate your pond temperature in the summer. However,  roots can pose a problem over time.

Roots don’t just add an extra layer of difficulty to the dig, they also naturally seek water and can damage the pond liner as they grow. If there is any defect in the liner, those roots that are looking for moisture will take advantage of any weaknesses.

If you decide to keep the tree (or trees) around, chopping away at a tree’s root system can also kill it. The damage might not be immediate, and it can take a number of years for your tree to die, but cutting the main root system is more than likely a death sentence for that tree.

The general rule of thumb is to multiply the diameter of the trunk (in inches) by 1.5 and that will give you the safe radius in feet for digging outside the tree’s buffer zone.

However, it is important to know what type of tree it is. Some tree’s root systems, like the Willow, can extend quite a long distance, making it more likely that you will harm the tree or the tree roots will harm your pond.

Liner

A pond liner is a material used to create a sealed and watertight barrier around the perimeter of your pond. There are number of liner options from which to choose:

  • polypropylene
  • EPDM
  • Prefab plastic
  • Concrete

You should consider each type carefully before you start to dig. What you intend your pond to look like can be influenced by the type of liner you use. Each can be chosen to suit budget, intended use and personal aesthetics.

When choosing your pond liner, it is important that you look at the quality of each, especially with the flexible fabrics. Weather resistance, especially resistance to UV rays and freezing temperatures, are important in the longevity of the liner.

Also, make sure that the liner is koi safe. In some cases, liners may have to be treated. Here is an article on how to cure cement for a koi pond.

Underlayment

Before the liner goes in, you will need to add a layer of “padding” between it and the earth. This stabilizes the liner and reduces the likelihood of a tear from rocks or rough material.

There are a number of different materials that pond builders will use for underlayment, including loose sand, newspaper, quilts and blankets, tarp, old carpet, a weed barrier, and geotextile.

The underlayment should be loose or untamped to allow for it to shift and settle when the liner goes over it.

Higher is Better

The higher the pond’s elevation, the less likely you are to get runoff in your pond. If you build in a natural basin or at the lowest point on your property, the runoff will likely end up in your pond.

Although runoff seems like the least of your problems, given predators, bugs and leaks (as well as being a chlorine-free water change), it can bring in materials that are harmful to your koi or create an imbalance in your healthy parameters.

Some of the things that runoff can introduce:

  • Debris
  • Phosphates
  • Nitrates
  • Sulfates
  • Pesticides
  • Heavy metals

Watch Videos

There are hundreds of hours of professional pond builders doing their thing online. You might not be able to do exactly like they do, but you might pick up some invaluable insights, as well as helpful tips and tricks. Use that expertise from the videos to better inform your own effort.

Expect Setbacks

There aren’t many construction projects that finish on schedule and exactly as planned. Anyone that has built or helped build a koi pond will tell you that not everything goes according to plan.

Roots, boulders and equipment failure are only a few things that you might unexpectedly pop up.

Don’t get discouraged. Keep on digging.

General Dig Tips

Keep these best practices in mind as you dig your first koi pond:

  • Hydrate, hydrate, hydrate: no matter what season you dig in, remember to stay well hydrated.
  • Loosen up: if you are doing the excavation by hand, make sure to limber up first. Nothing stops a koi pond as quickly as a a strain, pull or tear.
  • Have NSAIDs : digging can be back breaking work. Make sure you have some ibuprofen or similar medication on hand to help with inflammation from your labors.
  • Wear gloves: if you are determined to do this the old fashioned way and you’re not a professional pond builder, gloves can help with reducing blisters as well as bumps and nicks.

Plan Your Next Pond

You may as well. Once this pond is dug, lined, waterfalled, filtered, seasoned, filled and stocked, you are going to want to do it all over again.

Now that you have one, with mistakes made, lessons learned and the ideas for a new, better, bigger koi pond burning a hole in your subconscious (and bank balance), you will be better prepared to plan for the rebuild.

As complicated as it might seem—and sometimes can become, a koi pond can provide much-needed relaxation for koi keepers and a wonderful environment for their koi to thrive. So take your time and do it right.

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