Probably one of the most heart sinking moments in any koi kichi’s life is coming outside to see the water level in their koi pond so low that their living jewels are gasping for air. Then there is the astronomically high water bill that means someone opened a water theme park or the pond has a leak.

Either way, an invisible leak is the bane of a koi keeper’s existence.

Fortunately (if there is such a thing for large water losses), it is not usually a tear or hole in the liner. The most common culprits for water loss are:

  • Improper construction
  • Settling of backfill
  • Inadequate amount of liner around the edges
  • Bad or degraded plumbing connections
  • Faulty skimmer
  • Leaky filters
  • Waterfalls

Then you have to consider whether it is a leak, or you have an evaporation issue. So what is considered “normal evaporation”?

There are many factors that affect ”normal” rates of evaporation. So it becomes difficult to fashion a truly scientific methodology. Warmer, windy climates can see ponds lose upwards of 1” a day.

Koi pond with Fountain
Fountain, koi fish, garden, Koi Pond, Meditation Garden by Wonderlane cc 2.0

Some of the things that can affect the rate of water loss:

Pond-design issues

  • Waterfall design flaws
  • Type of water feature used
  • Length of stream
  • Splash out

Environmental factors

  • Wind
  • Relative humidity
  • Water plants
  • Wicking
  • Shaded vs unshaded
  • Cloud cover
  • Surface area

As you become a more seasoned koi pond veteran, you will notice seasonal patterns making it easier for you to determine if the water loss you are experiencing is cause for alarm or simply the combination of a lot of environmental and/or pond design circumstances.

As an exercise, mark off your surface levels and chart them on a daily basis. The longer you keep records the more accurately you will be able to diagnose whether it’s normal evaporation or something more sinister at work.

There are some means to help keep your pond at the right level that have both advantages and disadvantages (as forums will often testify to).

Fill Valves

If you are subject to water loss on a regular basis in your koi pond, a fill valve is a viable option. Once your pond falls to levels lower than that of the float in the tank, the water is turned on until the water level is back to the level you have set your float to shut the valve back up.

As hands free as this option is, it has two potential downsides.

First, fill valves have a tendency to stick, so without proper and routine maintenance it can result in either it not turning on when the water level drops, or then staying on even if the water level is at the right level (think: running toilet before you jiggle the handle).

Secondly, if you do have a leak, it masks that fact until you receive your water bill (which in some cases, only comes once every 3 months). This then pumps chlorinated water into your pond which can prove disastrous to your koi population if not checked frequently and regulated.

Constant Drip

There are some enthusiasts that use a constant drip as a form of water changes. The question then becomes similar to that above about the effects of adding chlorinated water consistently. With a drip fill, however, the rate of water flow into the pond is generally a lot slower than that of a rapid infusion. Also, adding a filter (similar to that on a fridge) can help to filter out the impurities.

Step 1. Check the Obvious

Sometimes the water loss can be easily explained. Check along the edge of your pond to see if there are any wet areas, especially around any features (waterfalls and fountains). It can even be a result of a fountain spraying water too high and it being blown out of the pond. Be thorough though. Even if it is a small spot, it can mean that you are still losing significant amounts of water.

Check the edge of the liner, too, to ensure that it hasn’t sunk under the water level. This can be something that happens after many years of no problems at all.

After you’ve looked and poked around the edge of your pond—eradicating all the usual suspects—you’ve discovered that you have a leak (yikes!). So, what’s next?

Step 2. Be patient

You are right to be concerned for the wellbeing of your koi, but panicking will not help them. You might be fortunate to find the leak very quickly and diagnose how to fix it. But finding the leak can be a time consuming process. Even the pro’s don’t always get it right the first time.

Step 3. Turn off the pumps

Koi pond leak in pipes
Courtesy: Premier Ponds

If it moves water, turn it off. So pumps, waterfalls or fountains all need to be turned off—while making sure that you still have adequate aeration for your koi. Your fish (and plants if there are any) rely on the oxygenation so you might have to add aerators.

This will help to determine if it is one of your water features or the pipes/hoses that are the source of the leak. If the water stays at the same level, then the problem is in your plumbing or equipment outside of your pond, and not your basin.

Finding the leak outside of your basin:

  • Look for obstructions in the waterfall weir causing the water to spill over the liner.
  • Check for wet areas around the water features again (one company even uses a plant moisture meter).
  • You can dig small “fill holes” around the waterfall, turn the pump back on and see which one fills up.
  • Eyeball all of your visible plumbing. Pay close attention to the joints.
  • Check both the fall box bulkhead fitting on the filter as well as the soil under it (the moisture probe is a good tool here).
  • Inspect the skimmer box for damage and retighten fittings.
  • Check the outlet tubing along the ground from the pump to the feature in question.
  • If you suspect it is the tubing, attach a shunt tube to the pump and run it to the waterfall. Turn the pump on again for a day. If the water level doesn’t drop then the tubing is your prime suspect.
  • If you have a stream, move the new tubing upstream and monitor the water level after a day. If it drops, move the hose down a few feet downstream and repeat the process until the level stays constant. Then you have a better idea of where in the stream the leak is.
TIP: Use PVC primer before you glue also, it bonds the pipe better than just glue.

Self-adhering Silicone Tape

This product, quite literally, bonds to itself when wrapped around a pipe that has a leak in it. The consensus is that it is good in hard to reach spots, but shouldn’t be considered a permanent solution for pipe leaks.

There can still be a combination of leaks so you will have to remain vigilant even once you think you have the leak licked.

Other Less-noted Leak Causes

  • In the tubing, sometimes a cold winter can cause it to freeze and crack at its lowest point.
  • Rodents are also a source of concern under stream and pond liners. In the winter months, rodents look at the area around your pond—especially under or around the liner—as a welcome port in the storm. Not only is it a good way to stay out of the elements but also a ready source of water when the ground water is frozen. They will burrow in behind the liner and peck holes in it to get to the water beneath the ice. When the warmer weather comes back, take a look for their leavings or other tell tale signs that you might have mice.
  • Incorrectly tamped dirt around or under a liner can cause it to sink below the water level. Over time, the dirt will settle, and as it does, the liner can start to dip below the water level.

Steps to Finding Leaks in the Basin

Once you have ruled out that your leak is coming from outside the pond itself, it’s time to get serious about finding out where the leak inside your basin is.

Let the water continue to leak out with the pump off. If it is getting to dangerous levels for your fish load, they will have to be relocated temporarily.

Use a small amount of milk or fish-friendly pond dye along the edge of the pond and watch to see if it’s drawn towards the leak. It works better for identifying bigger/faster leaks in the liner.

Once the water settles to a consistent level, examine the liner all the way around the basin. Make sure you are slow and careful. Even the smallest hole can drain a pond over time.

If it is a tear in the liner then you can patch it. There are a variety of materials available on the market. Experts have their favorites, but they all advocate for using a glue that is non-toxic to your fish and/or plants.

Regardless of the materials that you use, there are a couple of necessary steps to take before, during and after the patch application:

  • Make the hole “clean” by cutting away any jagged edges.
  • Scrub the liner so that it is dirt and algae free (if not, the glue might not stick correctly.
  • Clean it properly.
  • “Rough up” the liner and the patch adhering surfaces with sandpaper or a wire brush (it gives the glue more surface area to bond to).
  • Let it dry.
  • Make sure the liner is wrinkle free.
  • The patch needs to be 2-4” bigger on all sides than the hole.
  • Rounding off the corners is recommended.
  • Apply an activator to the clean and dry liner surface around the hole to the same dimensions as the patch.
  • Let it become “tacky” to the touch.
  • Add the glue to the patch.
  • Work from the inside of the patch outwards.
  • Roll out any air or bubbles. You can use a piece of PVC piping if you don’t have a roller.
  • Let it stand for 6-8 hours before adding water.
  • Fill up the pond to just above the patch and wait to see if it leaks.

This quick how-to video by the Pond Digger recommends taking care of tears in the liner before it is filled with water.

TIP: Experts recommend having anywhere from 4-6” of overlap when joining two separate pieces of liner in a stream or in the basin.

If you do find that you have a leak, remember that it is not the end of the world. It’s not quite as simple as fixing the tire on your 10 speed bike, but with a little patience and attention to detail, you can get the leak fixed up and your pond back to normal.

10 responses

  1. Nancy Hing :

    Hi I’m located in San Jose California. Do you know a contact for anyone to help me find the leak? I’ve tried many things and I still have a hard time seeking the cause of my leak


    1. Hi Nancy,

      Thank you for reaching out to us. We do apologize, as we are not pond building experts and are not able to throughly answer your question. We recommend contacting an Aquascape Pond Builder or Certified Aquascape Contractor in your area. They are much more knowledgable with pond builds and maintenance. You can try finding one via the link provided below.

      Thank you.

    1. Hi Scott,

      Thank you for reaching out to us. We do apologize, as we are not pond building experts and are not able to throughly answer your question. We recommend contacting an Aquascape Pond Builder or Certified Aquascape Contractor in your area. They are much more knowledgable with pond builds and maintenance. You can try finding one via the link provided below.

      Thank you.

  2. What brand of polyurethane is safe for the using around the patch…the last step

    1. We do apologize, as we are not pond building experts and are not able to answer your question on the brand recommendation. We recommend contacting an Aquascape Pond Builder or Certified Aquascape Contractor in your area. They are much more knowledgeable with pond builds and maintenance. You can try finding one via the link provided below.

      Thank you.

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