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Understanding Chloramine in Koi Ponds (Complete Beginner's Guide)
📘 Part of the Leeds Koi Knowledge Hub
Written by the Leeds Koi Team
Estimated Reading Time: ⏱️ 9 Minutes
This guide forms part of the Leeds Koi Knowledge Hub, our growing collection of beginner-friendly articles covering koi pond water quality, filtration, maintenance and fish health.
Whether you're new to koi keeping or maintaining an established pond, understanding chloramine is essential for protecting your koi and preserving the beneficial bacteria inside your biological filter.
Every article in our Knowledge Hub is written to help you build a healthier, safer and easier-to-maintain koi pond.
Many UK water companies now use chloramine instead of chlorine to disinfect drinking water before it reaches your home. While this makes tap water safer for people, chloramine can be extremely harmful to koi and the beneficial bacteria living inside your biological filter if it enters your pond untreated.
Unlike chlorine, chloramine is much more stable and remains active in the water for longer. It cannot simply be left to stand before use, meaning every water change must be treated correctly.
In this complete beginner's guide, you'll learn what chloramine is, why it's dangerous, how it affects your pond and the safest ways to remove it before adding fresh tap water.
💡 Leeds Koi Tip
Always assume your tap water contains chloramine unless you know otherwise. Using a quality water conditioner at every water change is one of the simplest ways to protect your koi.
What Is Chloramine?
Chloramine is a disinfectant created by combining chlorine with a small amount of ammonia.
Water companies increasingly use chloramine because it remains active much longer than chlorine while travelling through miles of underground water pipes.
Although this improves drinking water quality, it creates additional challenges for koi keepers because chloramine is much harder to remove than ordinary chlorine.
Why Is Chloramine Dangerous to Koi?
Chloramine affects koi in two ways.
- It damages delicate gill tissue.
- It harms the beneficial bacteria inside your biological filter.
- When neutralised, it releases ammonia into the water.
If untreated mains water enters your pond, your koi can quickly become stressed while your biological filtration may be weakened.
Even relatively small amounts added regularly during water changes can cause long-term problems.
💡 Leeds Koi Tip
Healthy koi rely on healthy filter bacteria. Protecting your biological filter is just as important as protecting your fish.
How Does Chloramine Affect Your Biological Filter?
Your biological filter contains billions of beneficial bacteria responsible for converting ammonia into nitrite and finally into nitrate.
These bacteria are extremely sensitive to disinfectants.
Repeated exposure to untreated chloramine can:
- Reduce bacterial colonies.
- Slow the nitrogen cycle.
- Cause ammonia spikes.
- Cause nitrite spikes.
- Reduce filter efficiency.
Protecting these bacteria is essential for maintaining excellent water quality throughout the year.
How Can You Tell If Your Water Supply Uses Chloramine?
Unfortunately, chloramine cannot usually be detected by sight or smell.
The easiest way to check is to:
- Visit your local water supplier's website.
- Read your annual water quality report.
- Contact your water company directly.
- Treat every water change as though chloramine is present.
Many koi keepers simply use a quality chloramine-removing conditioner every time they add mains water, regardless of which disinfectant their supplier currently uses.
💡 Leeds Koi Tip
Water companies can change between chlorine and chloramine without notice. Treating every water change provides peace of mind and maximum protection.
How Do You Remove Chloramine Safely?
Unlike chlorine, chloramine does not simply disappear if you leave tap water standing. It remains stable for much longer and must be actively neutralised before the water enters your pond.
The safest ways to remove chloramine include:
- Using a high-quality pond water conditioner that neutralises both chloramine and the ammonia released during treatment.
- Installing a specialist hose filter designed to remove chlorine and chloramine.
- Treating every litre of mains water before it reaches your pond.
- Adding fresh water slowly during water changes.
- Following the manufacturer's dosage instructions carefully.
Modern water conditioners work almost instantly, making them one of the easiest ways to protect both your koi and your biological filter.
💡 Leeds Koi Tip
Always choose a conditioner that specifically states it removes both chlorine and chloramine. This provides the best protection regardless of which disinfectant your local water supplier currently uses.
Should Every Water Change Be Treated?
Yes — every single one.
Whenever fresh mains water enters your pond, it should be treated before it comes into contact with your koi or biological filter.
This includes:
- Routine weekly water changes.
- Topping up water lost through evaporation.
- Large seasonal water changes.
- Emergency water additions.
- Automatic top-up systems.
Even small amounts of untreated chloramine added regularly can gradually damage beneficial bacteria and increase stress levels in your koi.
💡 Leeds Koi Tip
Making water conditioner part of your normal maintenance routine is one of the cheapest ways to avoid expensive water quality problems later.
Chloramine vs Chlorine
Although both chemicals disinfect drinking water, they behave very differently inside a koi pond.
Chloramine | Chlorine |
|---|---|
Made from chlorine and ammonia. | Single chlorine disinfectant. |
Remains active for much longer. | Dissipates more quickly. |
Cannot simply be left standing. | May naturally dissipate over time, although treatment is still recommended. |
Releases ammonia when neutralised. | Does not release ammonia. |
Requires conditioners designed for chloramine. | Neutralised by standard dechlorinators. |
Understanding the difference helps ensure you choose the correct products and avoid accidentally damaging your pond's biological filter.
💡 Leeds Koi Tip
If you're unsure whether your water supplier uses chlorine or chloramine, always treat your pond water as though it contains chloramine. It offers the highest level of protection.
Related Water Quality Guides
Understanding Chlorine in Koi Ponds
Learn how chlorine affects koi, damages beneficial bacteria and how to safely remove it during every pond water change.
Safe Water Changes for Koi Ponds
Discover the safest way to replace pond water while protecting your koi and preserving your biological filter.
🚰 Learn More About Safe Water Changes →
How to Test Koi Pond Water Correctly
Learn how to accurately test every important water parameter using liquid test kits and identify problems before they affect your koi.
🧪 Learn More About Water Testing →
Understanding Pond Water Test Results
Understand what your ammonia, nitrite, nitrate, pH, KH and GH readings mean and what action to take.
📊 Learn More About Water Test Results →
Recommended Products
Pond Water Conditioners
Neutralise chlorine and chloramine while detoxifying the ammonia released during treatment.
Hose Filters
Help remove chlorine, chloramine and other contaminants before fresh water enters your pond.
Water Test Kits
Monitor essential water parameters to keep your pond healthy all year round.
Digital Pond Thermometers
Monitor seasonal water temperature changes that affect koi health and biological filtration.
Final Thoughts
Chloramine is one of the most important tap water contaminants every koi keeper should understand. Because it is far more stable than chlorine and releases ammonia when neutralised, it requires the correct treatment products every time fresh mains water enters your pond.
By using a quality water conditioner, protecting your biological filter and carrying out safe water changes, you can confidently use mains water while maintaining a healthy environment for your koi.
Continue Learning
If you found this guide helpful, continue exploring our Water Quality articles or browse the complete Leeds Koi Knowledge Hub.
💧 Explore More Water Quality Guides
📚 Return to the Leeds Koi Knowledge Hub
Educational Disclaimer
The information provided in this guide is intended for educational purposes only. Every pond is different, and water quality can vary depending on filtration, stocking levels, maintenance and environmental conditions. Leeds Koi & Pond Centre accepts no liability for any loss, damage, illness, fish losses or equipment damage arising from the use of this information. Always follow manufacturers' instructions and seek professional advice where appropriate.
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