We’re all aware of chlorine’s disinfectant properties and its ability to keep our water system clean. This powerful halogen is helping us improve our daily lives in a variety of ways, but it is not without flaws.

Using chlorine to keep our water in mint condition saved us from a slew of diseases. Unfortunately, what is beneficial to humans can be harmful to fish and other aquatic life. Chlorinated water corrodes pool walls, causes chlorine poisoning, sickens your fish, and eventually kills them.

Continue reading if you want to learn more about the dangers of chlorine in pond water and what we should do about them.

Why is chlorine dangerous?

Among the many advantages of chlorine, the ability to disinfect water, keeping it odor-free and safe for swimming and human consumption is the most essential. It’s simple to use, provides residual anti-recontamination protection, and lowers the risk of diarrheal disease.

So, why is it dangerous then? Here’s why.

Chlorinated water kills bad bacteria as well as good bacteria that are necessary for the pond ecosystem.

Although a small amount of chlorine found in our drinking water won’t likely cause any problem for humans, it is extremely toxic to fishes and most aquatic organisms. And that can be lethal for your fish and plants.

Furthermore, chlorine can be corrosive to concrete and will damage the pool concrete.

Fortunately, there are now many ways you can easily remove chlorine and its derivatives from pond water and substitute it you can use to keep the water clean without facing the nasty side effects of chlorinated water.


So let’s talk about the dangers of chlorine in pond water and what can we do about them.

Dangers Of Chlorine In Pond Water

Dangers Of Chlorine in Pond Water

I know a pond owner uses to treat tap water but sometimes it has the opposite effect. Chlorine, as previously said, can be hazardous to your fish, plants, pool walls, and the entire aquatic system if you’re not careful using it. Let’s dig a little more into these drawbacks.


As easy and effective it may be, Chlorine can’t distinguish between good bacteria and bad bacteria. When added to the water, it eliminates both the bad bacteria as well as the good ones.

But for an aquatic system to thrive, beneficial bacteria are essential, especially for the pond’s biological filtration system. They reduce extra nutrients, fish wastes, sludge from the water and help prevent algae blooms.

So, killing these helpful bacteria, Chlorine causes the water quality to deteriorate and the waste level to rise. So, if you’re thinking to control harmful bacteria growth using chlorine, think again.

Pond Fish and other aquatic lives

How quickly and severely fish, tadpoles, plants, etc get affected depends on the level of chlorine in the water. At lower levels, fishes may not show any sign of irritation but it’s still harmful to them. Chlorine in high concentrations is fatal for pond fish and plants.

Because chlorine is an oxidant, it removes the essential slime coating from pond fishes and that causes stress and stress-related disorders.

Chlorine reacts with living tissues and organic substances, resulting in acute necrosis or cell death. Since the gills of fish are fragile and directly exposed to the aquatic environment, it causes nasty burns when it enters the gills. Gill necrosis can cause respiratory problems and asphyxiation.

Pond fish like koi and goldfish might show signs of chlorine poisoning by seeming stressed, irritated, gasping at the surface, or by trying to leave the water.  Affected pond fishes may appear pale, covered in mucus, and exhibit gill beats and hyperemia.

Concrete erosion

Chlorine causes damage and erosion to the pool walls. It can infiltrate concrete and reach the steel bars that provide structural support to the concrete. The chlorides damage the metal framework, putting the structure in jeopardy.

Human health

I know I said a small quantity of chlorine in our drinking water won’t be a threat to human health, you should know that it’s not without any challenges.

Some studies have shown that swimming in chlorinated water might be related to airway inflammation, risks of asthma, and some respiratory infections in children.

People have higher risks of developing different breathing problems or skin allergies due to continuous exposure to chlorinated water.

Chlorine-treated pools and hot tubs have pH levels that cause enamel erosion on your teeth.

So, if you ever wondered why your teeth are getting discolored or transparent in the front, notice allergy symptoms or breathing or eye problems after frequenting your chlorine-treated pool to cool off, now you know why.

By the way, I forgot to mention earlier but as chlorine kills off the useful bacterias too, the build-up of waste materials increases which throws off the water chemistry. As a result, chlorine becomes increasingly poisonous when the pH of the pond drops.

On top of that, the presence of phenols, a poisonous organic compound found in some types of organic wastes, can make chlorine exceedingly toxic when combined with it. So you might wanna keep that in mind too.

Anyway, now that we have a better understanding of the risks of chlorine in pond water than we had yesterday, it’s time to see what we can do about all these chlorinated problems of yours.

Chlorine vs. Chloramine

Before we move on to learn about dechlorinating the pond water and all that cool stuff, let’s make a quick stop to get to know this new thing called chloramine (it’s relevant, I promise).

Chlorine isn’t the only disinfectant in town now. Chloramine is a better and more effective contender and many companies are switching to that already. What makes chloramine better?

Well, chloramine treatment is a mix between both chlorine and ammonia. It is more stable than our good ol’ chlorine. This means it’s a better choice to efficiently treat tap water.

Also Chloramine, unlike straight chlorine, does not form a hazardous chemical compound named trihalomethanes that is toxic for the human body. Do you see why chloramine is gaining all these popularity points in public water sources?

It’s all very nice and good but the same factors that make chloramine so popular for water disinfection are now causing pond owners massive headaches. So, if you thought chlorine is bad for water, then buckle up! because this is gonna be so much worse.

Due to it being a gas by nature, chlorine doesn’t last long in the water. It evaporates after a while so its disinfectant effect doesn’t last long. You can easily bubble it out of the water by keeping it in a well-aerated container with a large surface area for several days.

But chloramine is much more stable and it can’t be bubbled out. It doesn’t evaporate, meaning the water stays disinfected for a longer period of time.

So, if you use chlorine neutralizing products (more on that later) on chloramine-treated water, it will only work the chlorine portion. And the ammonia can prove to be disastrous for your pond and its aquatic environment.

Even the smallest amount of ammonia in the water can cause gill damage in fish, pH imbalance, and offset the nitrogen cycle. And excess ammonia will be fatal for pretty much all kinds of aquatic lives.

So, before picking any neutralizer, first, make sure if your water is chlorine-treated or contains chloramine and take action accordingly.

How to dechlorinate the water in the pond: 6 Easy Solutions

Now that you know about chlorine, chloramine, and their harmful effect on your pond water, it’s time we talk about how to deal with them.

Chlorine and its derivatives can now be easily removed from water using a variety of methods, including de-chlorinator treatments, activated carbon filter chamber, and specialized filtration equipment. All of these techniques can remove chlorine residue from the water, making it far more comfortable and safe for goldfish, koi, and the rest of your pond’s ecosystem.

First and foremost, you always have to monitor and test the level of chlorine in the water. Since many water systems now contain chloramine, you should check with your water company and be sure of which disinfectant they are using. Then act accordingly. A lot of water companies use water conditioners, hopefully, the one you’re in contact with does the same.

Now, I have listed some of the ways you can dechlorinate your fish pond. Bear in mind that not all of these strategies would work for removing chloramine. I’ll make sure to clarify obviously but here’s how to dechlorinate pond water.

UV exposure

Starting with the most inexpensive one. For a small pond where only mild water change is needed, this is the easiest way. Just let the water sit out under the sun for 24-48 hours. This will give the chlorine enough time to reach the surface and evaporate in the atmosphere in an off-gassing process.

This is a good, budget-friendly way you can dechlorinate the water if you are working with a small pond or water container with fish. It works especially well if you’re in a hotter climate.

However, this method will not work if you want to remove chloramine. Unlike chlorine, chloramine doesn’t dissipate. So, if it’s chloramine you’re trying to remove, this method would be a sure fail.

Also, be mindful of how you leave the water to evaporate because it’ll take time and might get contaminated with other fallen debris.

Liquid Dechlorinators

The second and most common method of dechlorination is through the use of liquid Dechlorinators. They are capable of binding not only chlorine but chloramine and other substances too. So if you want a simple and environmentally friendly solution for your problem, you can use a liquid Dechlorinator that treats both.

These are suitables for small or large ponds alike, and you can treat the water multiple times to achieve the chlorine levels you want for your pond. They’re ideal for new ponds made entirely of municipal water, and you can use them to neutralize unwanted chemicals by changing the water before they disrupt the ecosystem.

Liquid Dechlorinators are very easy to use. Just pour enough product into the water when you top up, slosh the water around or circulate it with a pump and you’re done. The liquid Dechlorinator would do its magic and your pond would be chlorine-free in no time. You’ll find one of these in any local water treatment company.

Read the product descriptions and directions carefully to check what kind of substances it binds and how to use them.

If you suspect there’s still some residue left behind, most of these liquid Dechlorinators can be poured into the pond with the water already in it.

Here I’ve picked three Dechlorinators that will safely remove chlorine from a fish pond. Let’s have a look at what they have to offer.

CrystalClear Vanish Plus Liquid Dechlorinator

CrystalClear Vanish Plus Liquid Dechlorinator

First off, we have Vanish Plus liquid Dechlorinator by CrystalClear. Not only does it detoxify by immediately removing the chloramine, chlorine, ammonia, and other heavy metals from the water, it also works as a stress reducer.

Vanish Plus adds a slime coat protectant to the water, which will aid in the healing of wounds and abrasions while also safeguarding your fish during stressful situations like water changes and clean-outs.

It comes in a 32-ounce bottle and can treat up to 6400 Gallons of water. It’s safe for all kinds of land, aerial and aquatic lives.

API TAP Water Conditioner


API’s Tap water conditioner is a crowd favorite and rightfully so. Like any effective water conditioner, it rapidly neutralizes chlorine, chloramine, and any other potentially harmful chemical in the water. It also prevents gill destruction, tissue irritation, and fish death due to the pollutants.

Just like Vanish Plus, this conditioner is safe for all aquatic lives and you can use it in both fresh and saltwater. Be it during a new pond or aquarium set-up, water changes, or while adding the fish.

The formula is very concentrated and strong so you’ll only need up to 3ml to treat 10 gallons of water.  If you have a pond with a few hundred gallons, this is the one to go for.

Seachem Pond Prime Water Conditioner

Seachem Pond Prime Water Conditioner

Just as the two other Dechlorinator I’ve mentioned earlier, Seachem pond primer also removes chlorine chloramine from your aquatic environment. So what sets it apart from the other products?

Well, the Pond Prime is an all-in-one conditioner that provides essential ions while also stimulating the natural slime coat in any pond. It helps with detoxifying nitrite, nitrate, ammonia, or any heavy metals found in typical concentration levels of tap water.

Pond Prime, according to Seachem, is 5x more concentrated than competing products, and a 500ml bottle can treat over 10,000 gallons of water. And it does all of that without causing any pH drop or over-activation of skimmers.

So, these are the three products I thought you might find helpful. But if not, that’s okay too because there are plenty more fish in the pond.

Inline Dechlorinators

Don’t want to go through all these hassles and just want to get dechlorinated water at the touch of a button? Then you’d love an inline Dechlorinator. if you use a lot of tap water for a koi pond, a pond with an auto-top-up, or if you want chlorine-free tap water for other purposes, this is just the thing for you.

The Dechlorinator is installed between the outside tap and the hose’s termination, ensuring that all water flowing through the hose passes through it first. Water enters the unit through one end and is pumped through carbon, removing chlorine along the way.

Because it’s all about contact time, inline Dechlorinators will have a maximum flow rate listed. The slower you push water through the unit, the more time it spends in contact with the carbon inside. Some units are disposable once they’ve been used, whereas others may be opened and the carbon block filter replaced with a fresh one.

Activated carbon filtration

Another effective and cheap way to dechlorinate is using activated carbon filtration. Activated carbon is a means of  water filtration that removes heavy organic pollutants which isn’t possible by mechanical and biological filtration.

The carbon operates by ‘adsorption,’ causing things to adhere to the carbon’s surface. When the surface becomes saturated, the compounds bind to the carbon, get neutralized, and the carbon is finally replaced (around every 2-3 months).

Heavy substances like chlorine,  chloramines, pesticides, fragrances, medications, can all be eliminated with this method. You can use it on its own to purify water before pouring it into the pond or add it to your filter system to neutralize it for optimal results.

It can be used all year for greater filtration and has no real disadvantages besides the cost.

Activated carbon filtration is especially helpful for new ponds throughout the cycle process since it lowers chlorine levels and boosts beneficial bacteria populations, giving you a safe fish pond.

Water filtration systems

This can help you quickly and effectively remove chlorine from the water. There are many different types of pond filters, each with its pros and cons. The only downside to these is they tend to be much more expensive than the other methods.

Aerating sprayer

Use a aeration device to provide air to the water as it enters the pond to dechlorinate it. Chlorine is a gaseous substance that will evaporate spontaneously in open ponds, but aeration will quicken the process significantly.

Aeration does not work for chloramine because it’s heavy and less volatile.

Substitutes for chlorine in pond water

Chlorination to treat water has been around since the early 1900s. While we can’t deny its importance as a major disinfectant, we can’t ignore the risks it poses to human and aquatic life either. Both chlorine and chloramine are not the best for our ponds but pond owners don’t have too much of a choice due to the lack of better alternatives.

But luckily, with the advancement of science, now chlorine is not the only option we have while looking for ways to treat our drinking and pool water.

So, instead of using chlorine to purify your water, here I have some safer and effective options for you.


Bromine is a suitable alternative to chlorine for disinfecting your water, and it has certain advantages of its own. Just like its upstairs neighbor, bromine comes in tablet or granular form and effectively kills harmful bacteria from the water, minus the poisoning and irritation of course.

The main difference between chlorine and bromine is their work process. Chlorine attacks the impurities in the water and causes its chemical structure to change by taking away the electrons. This process is called oxidation. But oxidation does leave a waste product called chloramines behind which can be dangerous for the aquatic environment.

Whereas bromine functions by the ionization mechanism. It interacts with its adversary and completely breaks down the chemical structure, leaving no product behind (lack of oxidation might leave your pond water with a green tint though). Bromine also has a lower pH level so you do not have to worry about the water chemistry going off-balance.

Also if you own a spa, you should definitely pick bromine over chlorine as it does very well in high temperatures. Bromine functions slower than chlorine but it’s much more stable. And unlike chlorine, it doesn’t go away. I continue to work even after sanitizing your pool.

However, exposure to UV light breaks down bromine pretty quickly so you might want to keep that in consideration while looking for chlorine alternatives for your pond.


Another safe, commercially available, and effective disinfectant you can use instead of chlorine is ozone. This powerful oxidant is easily soluble in water and can eradicate a wide range of bacteria and contaminants over 3000 times faster than chlorine.

In the right quantities, ozone can treat all waterborne infections, whereas chlorine can’t (given practical, safe doses). Its disinfectant properties are not affected by pH, and the addition of ozone has no effect on the pH of water.

This oxidant functions as a micro-flocculent, allowing minerals like iron and manganese to be removed more easily. And you don’t have to worry about any noxious chemical odor, taste, or skin irritation.

An ozone generator or Ozonator is usually used to pump the ozone gas (in low concentration) into the filtration system and once the ozone is in contact with the water, it will break down all contaminants.

it won’t leave any long-term negative effect on the environment as some chemical water treatment does. Unlike chlorine, ozone does not leave any hazardous chlorinated by-products in the water, and it swiftly decomposes to pure oxygen when not in use, making it the most eco-friendly and long-lasting treatment technique.

Ozone is produced cost-effectively on-site and doesn’t need any extra storage. it’s becoming more affordable to install and maintain thanks to advancements in the technologies used to manufacture it. In most cases, an Ozone installation pays for itself in chlorine savings in less than a year.


Because of its complete incompatibility with chlorine, polyhexamethylene biguanide, or PHMB, is the best alternative available. It’s also the most gentle on human skin and aquatic life, as well as the safest.

The key benefit of PHMB over chlorine is that it is not an oxidant and its efficiency is not affected by sunlight or pH. Therefore, it’s quite stable and the concentration doesn’t fluctuate dramatically over time.

PHMB penetrates bacteria cell walls and makes them rupture from inside. Then it traps the particles in a thick gel which sinks to the pool’s bottom and gets sucked up by the vacuum system. To avoid a reaction with leftover chlorine, you’ll have to drain your pool and thoroughly rinse any pool equipment.

Products like Baquacil, Aqua silk uses PHMB as the active ingredient. But, since PHMB is not an oxidizer, you’ll need a 27% hydrogen peroxide shock treatment to accompany it for clarity. These products don’t cause any irritation but they can be pretty costly.

PHMB has relatively moderate coagulating capabilities that may produce insoluble particles in the presence of certain contaminants in the water. As the pool water flows, these insoluble are trapped in the filter. As the insoluble build-up in the filter, the backpressure may rise, requiring backwashing or a filter media rinse.

In addition, the filter should be chemically cleaned with a PHMB-compatible substance at least twice a season.

How to measure chlorine levels in the water

To control chlorine in the water, you need to monitor its level regularly. Chlorine may be detected with an electronic test device. In a pond, the ideal level of both chlorine and chloramine is 0.00 PPM or as near to zero as feasible. Now it is not possible to eliminate chlorine 100% so a target of roughly 0.01 PPM is an acceptable goal if your pond has fish.

Or you can simply test your tap water for how much ammonia is present in it, and if you find trace levels, you very certainly have chloramine as well. Testing isn’t usually necessary because at least one of the two will always be present in your mains water, and most commercial treatments can now remove both compounds.

Increase pond aeration for a few days if you fear chlorine damage to pond fish. This increases their chances of regaining their health. Sodium thiosulfate can easily neutralize chlorine in the water.

If you live in a hot climate with a lot of natural evaporation, you’ll be topping off your water more frequently, so you’ll need to be more cautious about chlorine levels than someone who lives in a colder region.

Also, treated water can be contaminated again if it comes in contact with things that have chlorine traces on them.

Final Words

Chlorine is good in terms of disinfecting and other stuff. But it can be lethal for aquatic environments and especially for your fish. This is why the dangers of chlorine in pond water are something you should always keep in the back of your mind as a pond owner.

Excessive chlorine kills fish if you don’t do anything about it; so, no matter what, always keep an eye on your pond’s chlorine level and make sure the water quality of your pond is ideal for your pond fish.

Similar Posts