Pond Maintenance

Koi keeping involves much more than simply building a pond and adding koi. Pond maintenance is a continual job that is critical to the overall health of your pond and pond population. Keeping your koi healthy means keeping your pond healthy.

We’ve put together this definitive guide to pond maintenance to help you make sure you have the right supplies, equipment, and upkeep schedule to keep your pond in the best shape possible.

Equipment and Supplies

A large part of pond maintenance involves keeping your pond water clean and healthy. The key to making this happen is ensuring that you have the right equipment to maintain your pond efficiently. Some equipment is essential for keeping your pond clean and koi healthy, while other supplies are optional but still very helpful.


Your pond pump is what keeps your water circulating. The constant motion helps keep water from becoming cloudy or dirty, and it adds oxygen to the water, which keeps your fish healthier.

Choosing A Pump

Pond pump models are either submersible or external. Submersible pumps tend to be the best choice for smaller, backyard ponds. They also are typically more cost-effective and much easier to install than external pumps. Pond pumps are sized by gallons per hour (GPH). To determine what size submersible pump will work for your pond, you’ll need to do a few calculations. This guide to sizing pond pumps can help you figure out which pump is a perfect fit for your pond.


Just as the name suggests, pond filters remove dirt, debris, and other pollutants that make the water dirty, and they are essential for keeping your pond water clean.

Choosing A Filter

There are two different types of filtration: mechanical and biological. Mechanical filtration removes larger, solid matter from your pond water, including fish waste, leaves, algae, and other debris. Biological filtration removes ammonia and nitrites from the water. For koi ponds, we suggest choosing a filter that has both mechanical and biological filtration capabilities. Mechanical filtration, or a skimmer, helps prevent the biological filtration media from becoming clogged, which ensures that it functions properly.

The size of your filtration system depends on the water volume of your pond. We recommend purchasing a pond filter that can process the volume of your pond two to four times every hour. For example, a filter for a 1,000-gallon pond should be able to filter 2,000 to 4,000 gallons of water every hour.


The health of both your pond and your koi is directly impacted by water temperature. Water temperature affects dissolved oxygen levels and influences how quickly organic materials break down in your pond, which influences water quality. The metabolism of koi is also regulated by water temperature, and monitoring the water temperature will help you adapt the feeding schedule for your fish throughout the seasons. Because the water temperature is so important to your pond, it’s essential to invest in a quality thermometer.

Choosing A Thermometer

There are two types of pond thermometers: sinking and floating. We recommend purchasing both, especially if you have a deeper pond, as this will allow you to monitor the temperature of your pond at different depths. The temperature towards the bottom of your pond can vary greatly from the surface temperature. By averaging the two thermometer readings, you can determine the overall temperature in your pond.

It’s a smart idea to invest in high-quality pond thermometers. As we mentioned before, water temperature is extremely important, so you want to make sure you’re using thermometers that are giving you the most accurate readings possible.

Water Test Kit

Water quality is everything, and just because the water in your pond looks clean doesn’t mean it is clean. Keeping your water healthy helps keep your koi healthy. A water test kit helps ensure that your pond water is in good shape by monitoring the levels of invisible toxins and pollutants.

Choosing A Water Test Kit

We suggest choosing a test kit that is made specifically for pond water. The solutions in each kit may not be different, but the reading cards for measuring pollutant levels may differ. Purchasing a kit made for pond water will ensure that the reading card is compatible with recommended pond water parameters, which will make the process much simpler. Choose a kit that measures ammonia, nitrite, nitrate, and pH levels.

Aeration Device

While some may argue that an aeration device isn’t technically essential, it’s extremely important. Oxygen is needed for the breakdown of waste and debris in your pond. Low levels of dissolved oxygen in your pond can increase the risk of illness in your koi. Adding an aeration device will keep dissolved oxygen in your pond at an optimal level, which will keep your water and koi healthy.

Choosing An Aeration Device

There are two main types of aeration devices: diffusers and agitators. Diffusers sit at the bottom of your pond and create bubbles that diffuse oxygen upwards. Since oxygen levels are always lowest towards the bottom of ponds, this type of aeration can be especially helpful for deeper ponds.

Agitators tend to be the more aesthetically pleasing option. These include water features that sit on or above the surface of the water, such as waterfalls and fountains. The best choice depends mostly on the depth of your pond. Diffusers tend to be the most popular and effective option for the majority of pond owners, but you can always install a water feature in addition to your other aeration device.

UV Clarifier or Sterilizer

The primary purpose of a UV clarifier or sterilizer is to prevent free-floating algae from building up in your pond. Algae itself won’t harm your fish, but over time the buildup of algae can cause a drop in oxygen levels, which can negatively impact the health of your koi. These devices use ultraviolet light to eliminate algae on the surface of your pond, as well as free-swimming bacteria and certain microorganisms.

The terms “clarifier” and “sterilizer” do not describe two different types of units, but rather two different functions on the same mechanism. A UV clarifier becomes a sterilizer when the flow rate is slowed. Algae cells can be killed fairly easily, so they don’t need to spend much time passing through the UV filter. If your primary goal is to make your pond water a bit less green, a UV clarifier should be enough. Other microorganisms are a bit trickier to eradicate, which means they need to pass through the UV filter more slowly. If your goal is to rid your pond water of certain viruses, protozoa, and other pathogens in the water, a UV sterilizer is the way to go.

Choosing A UV Clarifier or Sterilizer

Pay attention to wattage when choosing a UV filter for your pond. The larger your pond, the more wattage you’ll need. Most devices will have a chart on the box or website that will help you choose the right size filter for your pond. The other thing to keep in mind is whether you plan to use the filter as a sterilizer or clarifier. For example, as a clarifier, a 15W unit will work for a 2,000-gallon pond. But when used as a sterilizer, that same unit can only handle up to 500 gallons of water.

In addition to these few important equipment items, several other gadgets can make pond upkeep a bit easier.

Water Keeping

As we’ve mentioned before, water keeping is the backbone of pond maintenance. Healthy water means a healthy pond and healthy fish. It’s important to consistently monitor water parameters and know how to respond to any levels that may be off. The chart below outlines the ideal water chemistry levels for your pond water, and what you should do if they’re off.

Ideal Range

Typical Causes of Level Changes

Tips for Maintaining Optimal Levels

Ammonia (NH3)

<0.1 mg/l

  • “New tank syndrome” or unestablished biofilter.
  • Overwhelmed filtration system. The filtration system is either not strong enough for the size of your pond or your fish are producing more waste than the filter can handle.
  • Give the biofilter in a new pond at least a month to become established.
  • Feed koi smaller amounts or switch to a higher-quality, low-waste feed.
  • Ensure you aren’t overstocking your pond.
  • Make a big water change (up to 50%).

Nitrite (N02-)

<0.1 mg/l

  • If nitrite, ammonia, and nitrate levels are all high, your filtration system is likely overwhelmed. If it’s just nitrite and ammonia levels that are off, “new pond syndrome” is typically the issue.
  • Give the biofilter in a new pond at least a month to become established. Remember that a source of ammonia needs to be present to kick off the nitrogen cycle in your biofilter.

Nitrate (N03-)

<60 ppm

  • Excess waste, overcrowding, overfeeding
  • Reduce feedings or switch to a higher-quality, low-waste feed.
  • Add plants that reduce nitrates levels, such as watercress, irises, water lettuce, and water lilies.
  • Make a 10-25% water change

Dissolved Oxygen

>7 mg/l

  • Though technically possible, it’s very difficult for DO levels to be too high. Low levels are usually the result of overcrowding, heavy algae blooms, and rising water temperatures.
  • Add plants, which convert carbon dioxide to oxygen and can also provide shade for koi in warmer temperatures.
  • Add more aeration by installing a water feature or diffuser.



  • Excessive algae growth, external factors such as rainwater or runoff, breakdown of waste or sludge in the pond.
  • Avoid water changes of more than 10% when pH levels are fluctuating too much.
  • Control algae growth with a UV filter.
  • Use a pH stabilizer solution.
  • Baking soda can be added to pond to raise pH levels.

Maintenance Schedule: Tasks and Chores for a Healthy Pond

Setting up your pond with the right supplies and correct water parameters is only the first step. Even with all the necessary equipment, your koi pond still needs continual upkeep and monitoring. This includes performing regular maintenance tasks and routinely replacing certain equipment. Below, you’ll find a recommended maintenance schedule to help keep your pond in the best shape possible.

Ongoing Maintenance

Daily Tasks

  • Remove any leaves, debris, and excess food from the pond using a skimmer net.
  • Monitor koi, making note of any strange or concerning behaviors.
  • Check water temperature.

Weekly Tasks

  • Perform a 10% water change.
  • If you have a pond vacuum, check for debris build-up at the bottom of your pond and vacuum if necessary.
  • Clean out the skimmer basket.
  • Flush out the filter.
  • Check water parameters using the test kit and adjust any major fluctuations.

Seasonal Tasks

Fall (and Winter for climates that stay above 50°F)

  • Do a thorough cleaning of your pond, removing any sludge or debris build-up.
  • If leaves are an issue in your area, cover your pond with a net.
  • In colder climates, shut off water features when temperatures drop below 40°F
  • Bring tropical or subtropical plants indoors when temperatures dip below 50°F

Winter for Cold Climates

  • When water temperatures are around 45°F, remove the pump and filter and bring it indoors.
  • Drain plumbing to prevent freezing.
  • Add extra aeration to your pond to keep oxygen levels optimal.
  • If your pond is prone to freezing, consider installing a de-icer to prevent it from freezing over completely.


  • Do a thorough cleaning of your pond, removing any sludge or debris build-up.
  • Remove any winter equipment from your pond.
  • Reinstall your pump, filter, and any water features.
  • Perform a large water change, about 20%
  • To help reduce stress and illness in your koi, increase pond salinity to .3-.4%.
  • Switch on UV filter to help combat algae blooms.


  • Keep an eye on dissolved oxygen levels, as they can decrease quickly in warmer temperatures.
  • Add extra aeration to improve oxygen levels.
  • Ensure your pond has areas that are out of direct sunlight. This will help keep your koi cool and prevent sunburn.

Equipment Replacements

While your pond equipment is designed to be sturdy, it’s still prone to normal wear and tear. The exact lifespan of your pond equipment will vary, but the guidelines below should help give you a basic idea of when they may need to be replaced.


Typically needs replacing every…


5 years


5-10 years

Pond Liner

5 years

UV filter bulb

1 year

Water Pump

3-5 years

Water Test Kit

1 year

Pond maintenance does more than just keep your pond looking great, it is also vital to keeping your pond population healthy. It’s essential to set up your pond with all the necessary equipment and to implement a maintenance routine that keeps your pond functioning properly. With the right tools and the right upkeep schedule in place, you’re well on your way to being a koi-keeping pro.

Is your pond ready for a few new additions? Shop our Koi and Goldfish now.

8 responses

  1. Bernard Bronsink :

    I have 2 Koi that are 8 to 10 years old that the tail fin has a parasite eating the fin.
    I have 4 questions.
    1: Will a salt bath kill the parasite?
    2: I have 100 gallon tank to treat fish how much salt can I use without hurting the fish and how long do I leave them in the salt bath?
    3: Will the damaged tail grow back?
    4:There are 5 other Koi on the pond Soule they be treated as well?
    5: Is there a way to keep mink out of the pond last winter they ate 4 or 5 of our larger Koi?
    Thank you, the Koi I ordered from you are great and arrived healthy and are beautiful.
    Bernie Bronsink

    1. A salt bath may not necessarily kill the parasite. However, if you have a quarantine tank as you mentioned, you could isolate this fish and add it to the tank temporarily with salt in the water. We maintain a 0.35% salinity in all tanks in our facility, as it helps them build a thicker slime coat to protect themselves from bacteria and parasites. If you wish to replicate this same percentage, you would need to add approximately 3 pounds of pond salt to 100 gallons of water to achieve the 0.35% salinity. As for the mink issue, we have attached a link to another helpful blog article we have on this predator for you below.


      Thank you.

  2. Beverly Minyard :

    I like that you mentioned that there are daily tasks to owning a koi pond including removing all debris and excess food. My daughter really wants us to get a koi pond but my wife and I know that they require a lot of work. I think we will tell her that she would have to clean it every day and it might make her lose interest. https://grassrootspondandgarden.com/shop

  3. Ray Janus :

    I am considering converting our 18,000 gal pool into a koi pond. It has a maximum depth of about 5′. Would that be suitable for a larger koi pond. Our neighbor has a palo verde tree next door that has killed 2 pool pumps with the seeds that have been dropping into our pool. Would these seeds be a potential food source for the koi, or should I cover the pool to keep the seeds out of it. I have both options now.. (y)
    Just don’t want to maintain the pool these days as a swimming pool with the high cost of chemicals, etc.. (y)

  4. Eli Richardson :

    It really helped when you talked about ponds and how there’re different types of pumps for them. Recently, my sister said she wants to build a koi pond in her house’s backyard. My sister wants to know more about pond maintenance, so I’ll be sure to share your advice with her. Thanks for the information on ponds and how their pump requires maintenance.http://modernpumpinc.com/services/

  5. Edward Reeves :

    I appreciate the expert advice right here. Since https://purelyponds.com/maintenance/ just finished the project and landscaping at my Colorado Springs home last week, I actually am extremely new to Koi Fish and pond upkeep. The Koi I bought were incredibly lovely and pricey, so I definitely need to learn up on the subject!

  6. Afton Jackson :

    Testing and aerating a pond are two things I didn’t give much of a thought to until I read this article. If I don’t do this, the water of our pond could be unfit for some new fish after the winter season, and I bet that will really ruin the landscape as a whole. Once I find a pond maintenance expert in the area, I’ll make sure these are the kinds of things I’ll ask them for some help with.


  7. Quite an informative blog about pond maintenance. Your detailed guide is really helpful. I’d like to recommend a pond liner that is also a pond leakage-fixing quality product, it’s PondPro2000 a pond maintenance that’s also a butyl liquid rubber liner http://www.pondpro2000.com/epdm-pond-liner.php and easily can be applied to all types of surfaces. It’s a primer-free one-coat solution but still can last 3 times longer than other acrylic pond liners so you can choose this pond liner for fixing the leakage issues with your pond. It is a non-toxic, UV-resistant, and temperature-tolerant pond liner so is 100% safe for fish and plants in the pond.

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