How Long Does It Take Chlorine To Evaporate From Water? Essential Knowledge

If you are an aquarist, chances are you always have to worry about the quality of your tank’s water. If the water is chlorinated, your fish are not likely to survive and thrive. Hence, it is important to ensure that the aquarium is free of this harmful substance.

But how long does it take chlorine to evaporate from water? And why is chlorine detrimental to your tank? Let’s keep scrolling!

How Long Does It Take Chlorine To Evaporate From Water?

The exact number of hours needed for chlorine to evaporate from water depends on the water’s source, the water’s volume, and how much chlorine is present.

In most cases, a wait of at least 24 hours for this chemical substance to go away is recommended. Sometimes, the duration can be extended to nearly 5 days.

For water to be dechlorinated completely, a minimum wait of approximately 7 days is recommended.

Chlorine And Fish – Everything You Need To Know

What is chlorine

fresh water

Chlorine may purify drinking water

Chlorine does not always carry a negative connotation. In natural water, the amount of chlorine is almost unnoticeable. But water treatment processes require a calculated input of this chemical compound to clean and disinfect the water.

For humans to consume water safely, all germs and bacteria must be gotten rid of. Chlorination makes sure water remains healthy and drinkable, as it helps kill microorganisms responsible for multiple diseases.

Why is chlorine bad for fish?

If moderated carefully, chlorinated water is not a problem for humans. However, things are not the same with fish. Most species of fish will have their living tissues triggered and die upon exposure to chlorine.

Even the slightest amount of chlorine can cause organic matter and vital organs to shut down. Furthermore, both the external skin and the gills of your fish will be irreversibly damaged.

In short, your fish will fall prey to necrosis and fade away the moment you decide to add chlorine to their water.

In case you want to pinpoint the symptoms of chlorine poisoning, here are some of the most visible cues.

  • Rotten gills and skin surfaces: Your fish have tattered gills and their skin seems to be coming off.
  • Agitation: Your fish do not swim around idly. Instead, they move in chaos and even attempt to jump out of the water.
  • Weird body positioning: With internal organs shutting down and living tissues dead, your fish will present themselves in an awkward posture.
  • Hypoxia: Your fish struggle to breathe properly. You can no longer see bubbles coming out of their mouths.

Should your fish show any of these signs, it is time to remove them from the tank. Next up, make sure you treat the water carefully, so the next batch of fish does not suffer.

How To Remove Chlorine From Water

Removing chlorine from water merely requires a few days of waiting. But if you want to rush things and wish to create the perfect water conditions for your fish, below are some suggestions on how to fasten the process.


Using high temperatures to get rid of not only chlorine but also chloramine is arguably the cheapest and most efficient way. All you need to do is to transfer the tank water into a deep pan.

For every 10 gallons, 8 minutes of heating is a must. Repeat this procedure until the level of chlorine drops to almost zero. Wait for the water to cool down completely and put it back into the tank. Your fish should be ready to go within hours.

Carbon filter

Now, there are tons of carbon filters with activated carbon inside. The presence of this layer enhances water purification by removing chlorine as well as other toxins.

Rest assured that your fish will stay up and running once such a versatile filter is installed. But still, remember to keep the pH level in your tank balanced.

UV light

If you have money to spare and want the least invasive treatment for your tank’s water, nothing beats a UV light. With their radiant energy, UV rays coming out of a specialized bulb will get rid of chlorine and chloramine within minutes.

Ascorbic acid

In case you want to tighten the budget, using ascorbic acid is a fast and convenient way. By mixing ascorbic acid with water-based on a ratio of one tablespoon for every gallon, you get to enjoy how the former neutralizes the latter.

Even better, this type of acid does not interfere with your water’s oxygen concentration. Hence, there is no need to be concerned about whether the pH or hardness level is compromised.


1. How to test the chlorine level in water at home?

The most popular option is to buy a chlorine test kit. This product is available at all pharmacies and pet stores. With test strips designed to illuminate the chlorine concentration of your water, these test kits will give you a rough idea of your water’s conditions effortlessly.

2. Can I use bottled water for the fish tank?

Yes. Bottled water does not have chlorine, which makes it a safe option for your fish. However, you need to check out and see if bottled water contains any other chemical content. If you are not confident about their ingredients, consider using a water conditioner.

3. Can fish recover from chlorine exposure?

Can fish recover from chlorine exposure?

No. There has been no scientifically proven method for fish to recover successfully from chlorine exposure. Once they display symptoms of chlorine poisoning, it is best that you separate these sick fish and let them be on their own.


How long does it take chlorine to evaporate from water? Now you know the answer. Make sure to keep the water still for at least a few days before letting your fish swim inside it. This way, your entire tank will stay healthy!