Can You Keep Koi Fish in Tap Water?

Koi fish are gorgeous pets many owners keep in an outdoor pond or an indoor aquarium. However, they’re sensitive creatures that require clean, toxin-free water to thrive.

So, you can’t put koi fish in tap water. Most tap water contains bacteria-killing chlorine that can harm koi fish.

However, this doesn’t mean there aren’t solutions; as long as you remove chlorine, the water will be safe for the fish to swim in.

Why Is Chlorine Harmful to Koi Fish?

Chlorine is a harsh chemical element commonly used as a disinfectant. 

Water with chlorine is harmful to koi fish because it contains substances that kill bacteria.

Because chlorine can’t distinguish between harmful and good bacteria, it will destroy everything within the pond.

There are beneficial bacteria that are vital for the pond’s natural filtration system, and chlorine disturbs it, causing the water quality to decrease.

This chemical can also cause contact damage and respiratory problems to fish.

Koi fish that come in contact with it may experience scale damage, gill damage, and burns on their scales.

Chlorine may also enter its bloodstream, causing internal burning and intense pain for your aquatic pets.

How Much Chlorine Is Okay for Pond Water?

Ideally, your pond water should be as close to 0.00 ppm as possible. Unfortunately, even a tiny amount of this chemical can cause stress for your fish and doesn’t offer any benefit. 

Removing all of the chlorine or chloramine may be impossible in some cases. So, if you have around 0.01ppm in the body of water, it shouldn’t be an issue.

How to Measure Chlorine Levels

Measuring your pond for chlorine and other chemicals is essential for maintaining the health of the fish and other wildlife.

You can measure chlorine levels with an electronic testing device.

If your pond water tests positive for chlorine, you can increase aeration for a couple of days to improve the chance of your fish’s recovery.

You can also use water treatments to remove chloramines and chlorine safely.

Can You Top off a Pond With Tap Water?

You may need to top off your pond water in warm climates frequently. So, you’ll need to pay close attention to the water quality you use to top off your pond.

If you notice the water levels are low, you can top it off with tap water as long as you treat it before using it. However, you should never add untreated tap water to your pond.

Can You Top off an Aquarium With Tap Water?

Like with ponds, you should never add tap water to an aquarium. If your tank’s water levels look low, it may be time for a partial water change.

If you decide to add water to their enclosure, add chlorine-free water that matches the aquarium’s temperature precisely. 

How To Remove Chlorine From Tap Water

If it’s time to top off the tap water in your pond or prepare it for koi fish, you may feel tempted to use tap water.

Fortunately, there are several ways to treat tap water so your fish can swim safely.

Boiling the Water

You may heat the water to remove the chemicals for small replenishing needs.

Boiling water allows the chlorine to evaporate away, leaving you with fresh, clean, and safe water for your fish.

Once the water boils for at least 15 minutes, turn off the heat and let the water cool down completely.

Don’t ever add boiling hot water to your pond or aquarium; you want the temperature to be as close as possible to the pond temperature.

Use a Water Distiller

Most water distillers can remove around 97% of chlorine, though you can add carbon filters to bump it up to 99% removal.

Distillation works because chlorine gas weighs less than air at room temperature.

When a distiller heats, the element is light enough to leave through the device’s vents.

Water distillers also remove iodine ions, astatine, fluorine, and bromine, and many can extract various forms of pollutants.

Although most distillers focus on purifying water for drinking and are on the small side, there are more substantial options you may use to filter several gallons at a time.

Let It Evaporate

If you’re filling up a pond or tank without any fish, you can let the water evaporate and treat itself.

When chlorine hits the air, the molecules scatter and eventually vaporize out of the water. 

Although heat can speed up the process, you can let the water sit in the pond before adding any fish.

Let the water sit for at least one to two days, though it can evaporate more quickly in warmer environments.

Before adding your koi fish, test the water to ensure all the chemicals are released.

Every pond size and environment’s temperature varies, so it may take more or less time for the chlorine to evaporate in your area.

If you already have koi fish in your pond, it’s best not to use the evaporation method. Even if chlorine releases relatively quickly, you risk harming your koi fish.

Use a Chemical Neutralizer

Several chlorine-neutralizing products on the market are specially formulated to remove chlorine without disrupting water hardness levels, alkalinity, or pH.

When using this product, it’s best to place the fish in a safe space with clean water while you treat the pond water.

You may also use a neutralizer before adding your koi fish to speed up the process if you don’t want to wait for the chlorine to evaporate or have to treat gallons of water at a time.

What Type of Water Is Best for Koi?

Koi fish come from parts of Asia, swimming in fresh bodies of water in the Caspian, Black, and Aral seas.

They prefer water that has a diverse range of minerals, so adding salt and minerals to distilled water is ideal to ensure they thrive.

These cold-water fish thrive in temperatures between 59 and 77 degrees Fahrenheit.

So, if you’re building a koi fish pond, ensure there are plenty of shallow areas where they can cool down in the summer months or avoid freezing in the winter months.

Your pond water should be clean and ready to go before adding in koi fish; the worst thing you can do is add water directly.

Once you treat the water, introduce your fish to the water properly to avoid shock. 

Introducing Koi in a Pond With New Water

  1. Let koi fish sit in the bag for roughly 20 minutes before you slowly open the bag.
  2. Add some of the pond water into the bag and allow the koi to adjust to its new water for a few minutes.
  3. Gently place your koi fish into the pond.

Introducing Koi in Aquariums With New Water

  1. Place the bag with the koi fish in the aquarium, keeping the bag sealed.
  2. Allow the koi fish to adjust to the new temperature of the tank.
  3. Slowly release the fish and water into the aquarium.

Signs of Poor Water Quality for Koi Fish

Keep an eye on your fish as you would any pet. Koi fish will show distress if they struggle with poor water quality.

Look out for the following:

  • Difficulty swimming
  • Isolating and avoiding other fish
  • Not eating
  • “Gasping” for air
  • Lying on the bottom of the aquarium or pond
  • Laying on its side

If you notice your fish acting strangely, it’s time to check the water quality and make changes as needed.

Frequently Asked Questions

Here are the most commonly asked questions regarding “can you put koi fish in tap water?”

How long can koi survive in tap water?

If you place your koi fish in a pond or aquarium of tap water, your fish may die within an hour. 

Even if they survive through the evaporation period, they will likely have respiratory issues or damage to their bodies.

Can koi live without a pump?

Koi fish need oxygenated water to survive. Koi fish can survive without an oxygen supply that ranges from a few hours to a few days.

However, if there is no dissolved oxygen within the water, it will die within minutes.

How often should I change the water in my koi pond?

To keep your koi fish healthy and thriving, performing at least a 10-20% weekly water change is best.

However, more substantial water changes are even better for your fish’s health.

Can koi fish live in dirty water?

Although koi fish can survive in some dirty waters for short periods, they won’t thrive.

Some pollutants can be deadly to your fish or cause them to suffer illnesses that shorten their lifespan.

Are koi fish hard to keep alive?

Koi fish aren’t hard, but they’re not the easiest fish to care for.

You must perform regular water changes, provide aeration, and ensure they eat a well-balanced diet.

Final Thoughts

Koi fish are attractive pets you can keep inside an aquarium or outdoor pond. You can put koi fish in tap water if you treat it first.

Placing koi fish directly in tap water can cause damage to their bodies, cause respiratory issues, and even be fatal.

You may boil tap water or let it evaporate before using it for your fish. There are also products on the market created to remove harmful chemicals like chlorine from the water. 

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