How To Keep Your Fish Safe From Chlorine And Chloramine

Photo of author
Written By Mark Washburn

Mark has 20 years of experience as a professional pond management consultant.

Pond Talk is an Amazon Associate. As an Amazon Associate we earn from qualifying purchases.

Chlorine and chloramines are two things you certainly don’t want to have in any fish pond.  Both can be highly toxic to fish but they are also a common additive to every public or municipal water supply in the United States.

Chlorine, and the more recently developed Chloramine (which is chlorine and ammonia mixed together), are considered the gold standard for water sanitation in developed countries.  Chlorine was first used for water disinfection as far back as 1929 in the United States.  Both chemicals are excellent at destroying dangerous bacteria in public water supplies and this keeps the general populous safe from a number of water-borne diseases such as salmonella, cholera, giardia, and dysentery, just to name a few.

The problem for those with fish ponds however is that both chemicals are extremely dangerous for koi and goldfish.  In truth, no fish is really immune to the effects of these additives, and they make most tap water unsafe for direct use in a pond with fish.

How Much Chlorine Is Dangerous For My Fish?

Chlorine, as well as Chloramine, should be considered highly toxic to fish and other aquatic life.  The CDC notes that for drinking water, levels of either disinfectant, are considered safe up to 4 parts per million. Most municipal water supplies maintain chlorine levels of around 1.5 to 2.0 ppm, which is what you’d commonly find in your tap water.  However, chlorine (and chloramine) has been shown to be lethal to fish, even at low levels, ranging from 0.1 ppm to 0.3 ppm.

Fish, as well as other aquatic inhabitants like amphibians, absorb water directly into their bloodstream, making them highly vulnerable to chlorine poisoning.  Mammals and birds are not considered as sensitive.

Fish may initially exhibit over-exposure to chlorine through different kinds of hyper-activity.  Jumping out of the water, spasms, and just extremely unusual movements and behavior.  They may also show signs of respiration problems despite adequate levels of dissolved oxygen in the pond.  Left unattended, the exposure to chlorine will usually lead to skin and gill damage, as well as internal trauma from absorption of the chemical.  Therefore many fish can die from even low-level exposure to chlorine and chloramine.

With all of this in mind, I don’t consider any level of either disinfectant to be acceptable or safe in a fish pond.

Testing For Chlorine and Chloramine in Pond Water

If you are using residential tap water or water from a municipal source, you can be pretty certain that the water will contain at least low levels of disinfectants.  It might seem unnecessary therefore to test the water, but in my opinion, it’s still a good idea to first, see what levels of chlorine and/or chloramine are present, and second, do a follow-up test to verify that your process of removal (which we’ll discuss below) has been successful.

There are different ways to test the chemicals, but the simplest way is through a dip strip test.  You want a test for both free and total chlorine levels.  Keep in mind this tests for chlorine only, but you can calculate the level of chloramine by subtracting the free chlorine level reading from the total chlorine level reading.  Another way to secondarily test for chloramine is using an ammonia test.  If ammonia is present in the tap water, you can be pretty sure chloramine is the source of that.  Personally, I prefer simply testing for the free and total chlorine itself.

As mentioned previously the ideal level of these chemicals in a pond with fish is zero, but research has shown that a very low level of 0.01 ppm, is acceptable and tolerated by fish.

How To Remove Chlorine And Chloramine From Pond Water

Before addressing the best ways to remove chlorine and chloramine from pond water, I do want to note that, although they are used for water disinfection, and they are similar in how they do that work, there is one notable difference between them.  Chloramine is designed to last much longer between applications.  By comparison, chlorine will precipitate out of the water more quickly.  This allows some pond owners to simply use the passing of time to clear the water of the disinfectant.

When To Allow Water To Stand For Up To 48 Hours

It has been widely reported that when adding water to fill a pond, or to top off a pond, and chlorine is present in the source water, all one has to do is wait about 24 to 48 hours to allow it to dissipate.  There is some truth to this statement but this approach comes with a few caveats.

I think this time frame can work most often when used for adding a limited amount of water to top off a pond that has lost some volume due to evaporation.  By holding the water in a bucket and allowing it to breathe for a day or two, most if not all of the chlorine should be gone.

The same may not apply when filling a pond fully with new water.  In some cases,  it was reported that the chlorine level only dropped a slight amount over a 24 hour period, and at 48 hours there were still chlorine readings that indicated the pond would not be safe for fish.  In these cases, it could be that the chlorine had been mixed in part with some chloramines as well, which would prolong the evaporation from the water.

My advice: When using time, or any form of chlorine or chloramine mitigation listed below, I will routinely check the water I’m going to be adding to a pond.  In doing so, I ensure that regardless of what the treatment facility may use, or the condition of my prefilters might be, I’m able to keep the fish safe.

Liquid Or Powdered Pond Dechlorinators

The most widely used type of product for dechlorination of fish ponds would be a type of additive, either in powder or liquid form, that will neutralize chlorine.  Some of these might also be labeled as water conditioners, such as this one from Pond First.  It works well on chlorine and chloramines and will detoxify ammonia too.

If you happen to find that your source water is high in metals, as well as disinfectants, you might consider trying this neutralizer from API which is indicated to be effective on chlorine, chloramines, copper, lead, and zinc.

Activated Carbon

Another very popular and well-known pond additive is activated carbon.  This product is actually derived from activated charcoal, and this serves as an excellent binder for a number of unwanted things you might find in a pond.   This is the main reason it is commonly used in filter media, but it can also be added to the pond independent of a pond filter.

Activated carbon works by adhesion, and will readily bind to substances like chemical pesticides, insecticides, algaecides, as well as tannins (which can discolor pond water), and of course chlorine and chloramine.  Once bound to the carbon, they are all effectively taken out of the water column.

Activated carbon will also help with various off-odors coming from the pond and often improve water clarity as well.

Dechlorinating Hose Filters

In recent years I’ve been recommending dechlorinating filters to small pond owners.  These contain activated carbon and attach conveniently to a garden hose, and they do a good job of filtering out both chlorine and chloramines as the water is being added to the pond.  I find this filter to be most useful when topping off the water, especially if you find the need to add water routinely every day, which seems to happen to me often during the hottest summer months.

Currently, I recommend the Boogie Blue filter as its rated for up to 45,000 gallons before needing to be replaced, and it is reported to filter out up to 99% of chlorine and 87% of chloramine.  Since it uses carbon as the internal media it will also help with pesticides and other chemicals in the source water.

Here’s a tip that we’ve used with other carbon filters in the past. The maximum flow rate of the Boogie Blue filter is listed at 4.5 gallons per minute, however, for potentially improved filtering, you may want to try slowing the flow rate down by about half and see if you can achieve even better results with decontamination.

I always advise doing your own testing of the output water on a regular basis.  Carbon filters should typically be changed out yearly, and the output should be monitored, particularly as you close in on the rated gallon capacity noted by the manufacturer.  One simple way to keep track of your usage is to install an inexpensive, digital water meter between the garden hose and filter.

Whole House Multi-Stage Water Filtration Systems

For those with larger koi and fish ponds, or anyone who simply wants to make water dechlorination a bit easier around the home, it may be worth considering a multi-stage, whole house filtration system.

Although the cost is a bit more than the other options, this two-stage filter can make a lot of sense if you find yourself going through a lot of treatments or smaller filters over time.  Rated at 100,000-gallon capacity, the filter will remove 99% of chlorine along with other contaminants.  Like the other methods I’ve discussed here, it uses a carbon-based filter for dechlorination, as well as a second filter for fine sediment removal.

Of course, when installed on the mainline, this filter has the added benefit of removing chlorine from all the water used in the home, which many people view as a healthy option for drinking, bathing, cooking, and laundry use.  Unlike a reverse osmosis system, this filter does not reduce total dissolved solids, thereby keeping most healthy minerals in the source water.

Fortunately, as fish pond owners, we have a handful of good options when it comes to getting chlorine out of our pond water.  Most are carbon-based and work well, plus they are very safe to use too.  In the end, we can enjoy a pond with clear and healthy water and happier fish as a result.

Amazon and the Amazon logo are trademarks of, Inc, or its affiliates.