How Long Does It Take for Dechlorinator to Work?

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Chlorine is an effective and widespread fish killer that acts fast and can deliver devastating results.

The most common source of chlorine is tap water which many people use when performing their regular weekly water changes. Or when cycling the tank for the first time, for that matter.

Both of these instances are great opportunities for chlorine to poison the tank water and kill any fish and invertebrates you might be housing.

To prevent this, you should always dechlorinate the water before using it.

The best way to do that is via a professional dechlorinator, designed specifically for situations like this.

So, let’s see how dechlorinators work and how you should use them.

How Does a Dechlorinator Work?

Most dechlorinators contain sodium thiosulfate. This chemical has widespread uses, including in medicine, as part of treating cyanide poisoning.

It’s also the primary chemical to use in the aquarium business to neutralize chlorine and other heavy metals and dangerous chemicals.

Sodium thiosulfate achieves this by binding to the chlorine molecules and producing hydrogen chloride, sulfur, and sodium sulfate as byproducts.

Hydrogen chloride is harmless to fish, while the other 2 chemicals will dissipate quickly from the water.

How to Use a Dechlorinator in Fish Tank?

First, you should keep in mind that dechlorinators are all different. Some products are more concentrated than others, so you should always check the label prior to using your dechlorinator.

As a general rule, less concentrated solutions go for 2 drops per 1 gallon of water, while more concentrated ones go for 1 drop per 2 gallons of water.

You should always check the product’s label just to be sure.

If you’re performing a water change, pour the necessary amount of dechlorinator into the bucket containing the water you plan on using.

Dose the solution properly, wait it out to take effect, and then you’re free to pour the water into the tank.

How Long it Takes for Dechlorinator to Work in Fish Tank?

A good dechlorinator should take more than a couple of minutes to neutralize chlorine in the target container.

The quantity of water doesn’t matter because the more water you have, the more dechlorinator you’ll be using anyway.

That being said, dechlorinators need approximately 5 minutes to neutralize chloramines and other heavy metals.

So, give it extra time to take full effect before using the water.

Pros & Cons of Using Dechlorinator

The main pro of using a dechlorinator is fairly obvious – removing chlorine, chloramine, and other toxic agents.

But it’s the cons that we need to discuss here because many people are not aware of these.

They think that all dechlorinators are inherently beneficial, given that they’re designed to be used in fish tanks, but that’s not entirely true.

Here’s what I mean by that:

Cons of Using Dechlorinators:

  • Ammonia neutralizers – Some dechlorinators have special additives designed to remove excess ammonia. The problem is that these additives will also destroy your tank’s beneficial bacteria. This will create even more problems along the way, including drastic increases in ammonia and nitrites, which is ironic, to say the least. So, never use these types of dechlorinators directly on your fish water.
  • Skipping chloramine – Chloramine is also a damaging chemical that can poison your fish and invertebrates. Most dechlorinators neutralize chloramine too, but not all will. You want to get a dechlorinator that also addresses chloramine, so you should read the product’s label carefully before purchasing it.
  • Fancy dechlorinators – Many products have a variety of unnecessary additives, trying to fix as many chemical problems as possible in one go. This ‘all-in-one’ mentality may sound appealing, but it’s actually harmful in the grand scheme of things. Keep things simpler and only get clean dechlorinators without any fancy added chemicals that could cause system imbalances along the way.

Also, be careful how you’re dosing the substance. More is not always better.

Dechlorinator Alternatives

I understand why many people would skip dechlorinators altogether. Especially considering the downsides that we’ve just mentioned.

Fortunately, there are some viable dechlorinator alternatives worth considering.

These include:

Allow the Water to Breathe

Fun fact: chlorine dissipates naturally from the water. You only need to leave your water to ‘breathe’ for a while to allow the chlorine to dissipate completely.

This can last between 24 and 48 hours, depending on how much water we’re talking about. I recommend placing the water in a container with a wider open surface area for ease of dissipation.

Then you simply need to wait for Mother Nature to do its work.

Make sure you keep the container safe from any chemical contaminants, insects, or bacteria that may crawl in.

Boil the Water

Boiling the water removes chlorine and chloramine fairly fast. It should take 20-25 minutes max to get the job done.

The downside is that you’ll have to wait for the water to cool off before using it.

And, no, boiling the water doesn’t reduce its oxygen content, nor does it strip it of any minerals.

These are just online myths that you can easily ignore.

Vitamin C

This is probably the most popular dechlorinating method. Vitamin C neutralizes chlorine immediately and works well no matter how much water you have.

The recommended dose is around one teaspoon per gallon of water.

Don’t worry, vitamin C doesn’t affect your fish in any way. Just let the water sit for about an hour and test it to check chlorine levels.

It’s also worth mentioning that vitamin C is only effective in dealing with chlorine, but not much else.

So, don’t use vitamin C as a reliable chemical filtration solution because it’s not.


Chlorine is extremely dangerous to your aquarium fish and invertebrates, even in small quantities.

You should always check your fish’s water for chlorine and other dangerous heavy metals and contaminants since you never know when these substances can appear in the tank water.

This most often happens during improper water changes and due to adding contaminated elements to the tank.

I’ve written a more extensive guiding article on the topic, explaining how you should sterilize plants and other tank elements before adding them to your fish’s environment.

You might want to check that one too.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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