Koi is one of the loveliest backyard pond fish that you could ever have. They are pretty and hardy. Meaning they are great for fishkeeping, and at the same time, they elevate your backyard’s aesthetic value. But that only happens if they’re well-raised.

To keep Koi in their best condition, you need to have the pond at a pH level they’re comfortable with. When the pH is too high, Koi often suffers from Alkalosis, which could even bring fatal results.

You can lower your Koi pond’s pH by adding chemicals (i.e. White Vinegar, Alum) or organic matters or performing a water change.  

Eager to learn more about how to lower pH in a Koi Pond? Head down below.

What is pH?

In simple terms, pH is the amount of free hydrogen ion present in the water. It shows how acidic, alkaline, or neutral the water is.

When the pH is between 0 to 6.99, it means that the water is acidic. On the other hand, having a pH between 7.01 to 14 means alkaline. An exact pH of 7.0 is neutral.

For a change of one digit, there is a tenfold difference in the acidity or alkalinity of a pond. If your pond’s pH changes more than one digit, it indicates a drastic change and needs urgent observation.

Typically an acceptable pH range for koi ponds is between 7.0 to 8.6.

In order to maintain the appropriate pH in your Koi pond, you’ll have to test the pond water regularly on a weekly basis. The easiest way to do so is to get a pond pH testing kit from a nearby pond or garden store. While purchasing the testing kit, you’ll be supplied with a pH color chart as well.


Collect a sample of your pond water with a mug or cup. Now dip a chemically treated strip into the water and check the color of the paper. You’ll find out the pH level of the sample water by matching the color of the testing strip with the pH color chart.

After finding out the pH of your pond, you can proceed to adjust it. I’ll suggest checking your pond twice every day, in the same weather condition if possible.

How to Lower pH in a Koi Pond

Ways to lower the pH of your Koi Pond

Lowering the ph of your pond water is not a hard thing. You can do it in a few ways, but I’ll share the most efficient ideas with you down below:

Adding Vinegar

You can use white vinegar to lower the pH level of your pond water. But you’ll have to use it carefully. Do not spray vinegar directly towards your fish in the water.

If the testing kit shows that the pH is higher than 7.5, you’ll need to apply 59 ml or ¼ cup of vinegar for every 500 gallons. Now you’ll have to wait patiently to allow adjustments in the system. Vinegar will help to counteract the alkalinity in your koi pond water.

Re-test the water 12 hours later. If the pH level still hasn’t reduced to 7.5, you’ll have to continue applying vinegar. Keep repeating the application until the testing kit displays a pH that’s 7.5 or lower.

Applying Alum

You can also apply Alum to lower the pH of your Koi pond. Alum is a comparatively economical chemical that reduces your pond’s pH rapidly by reacting in the water to form acid.

Start with an initial dose of 27 pounds of alum per acre-foot of water. Apply an additional amount of 14-27 pounds of alum per acre-foot of water if needed.

However, it is necessary to check the water’s alkalinity before spraying Alum over the pond surface. If the alkalinity level is below 20 mg/L as CaCO3, you should avoid using Alum as it has the potential to increase the acidity in the water and decrease the pH in a dangerous way.

Increasing Carbon dioxide level

Carbon dioxide can also act as the acid in your Koi pond & help to reduce the pH level. You can add organic materials, i.e. soybean meal, cracked corn, or cottonseed meal, to increase carbon dioxide in your pond.

This method of decayed organic matter releasing Carbon dioxide doesn’t lower the pH level instantly but it is a safer & longer-lasting way.

You can stop your pond’s pH level from increasing by applying 15 pounds per acre of the organic matter daily for a week. There is no problem in adding other regular applications of organic materials along with the above-mentioned practice.

However, it is also essential to keep in mind that decayed organic materials also use dissolved oxygen. So the daily total of organic matter application should not surpass 50 pounds per acre as they can lower the concentration level of dissolved oxygen in a threatening way.

Partial Water Change

You can lower the pH level by performing a partial water change in your koi pond. Replace 10%-20% water of the pond with fresh water. It will also solve other problems related to a Koi pond, such as overgrowth of algae, high amount of chemicals (i.e. Ammonia)  in the water.

pH Clarifier

You can also purchase commercial products to reduce pH levels and help to circulate the water. For example, you can use clarity defense. It is a water clarifier that adds trace minerals to help make a balanced pH level in the water of your koi pond.

Additional Protective Measures

As mentioned earlier, having a high pH in your pond water means that the Koi are bound to experience Alkalosis, which is really difficult to alter. So it is also essential to take preventive measures as much as possible to maintain a balanced pH.

Curing the cement of the pond: You should cure the cement of your pond correctly before installation. If the cement is not cured, it involves the risk of toxic lime getting leaked from the pond embankment and increasing the pH of your pond water.

Controlling Algae Overgrowth: Before starting the application to reduce the pH level of the water, you should get rid of the algae from your pond. The overgrowth of Algae increases the pH of a pond as they absorb carbon dioxide and other chemical compounds for the purpose of photosynthesis.

You can use a UV Clarifier to control the situation. You’ll be able to remove all algae from your pond by running the clarifier for a couple of days.

Testing Tap Water: It is essential to test your tap water. Because if it has a high pH, it can affect your koi pond. So you should be careful that the quality of the tap water is not incompatible with the usage of your koi pond. You can remove the source of your water to somewhere else to guarantee the safety of koi.

Knowing when to Remove the Koi: When the pond water’s pH level is above 10, remove the Koi to a tank in your house because a high pH of that level could turn out to be life-threatening for the Koi.

Problems of high pH level koi ponds

As I’ve previously mentioned, you need your pond’s pH level to be inside 7.0-8.6; if it goes higher, the fish start to encounter Alkalosis. These are the symptoms a koi struck by alkalosis will display:

  1. Lack of appetite
  2. Excess slime production
  3. Bloody fins
  4. Resting frequently at the bottom
  5. Coming out to the surface while gasping
  6. Isolation

And, finally, it’ll succumb to death.

It is an irreversible condition, so there’s hardly anything you can do once it starts. So the best course of action is – Prevention.

High pH also leads to an abundance of ammonia. Excess ammonia is never a good thing as it can turn into toxicity and could result in serious health issues for your koi.

Final Words

The pH level of your pond water has a profound effect on Koi. Frequent changes in pH are not healthy for them. While taking necessary steps to lower the pH of your Koi pond, you ought to keep in mind that it should not head toward a pH crash. The water should not be too alkaline or too acidic. So always try to maintain a standard pH that suits them.

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