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When you use tap water to set up a new fish tank, you might be wondering how long it takes to dechlorinate tap water?

Here’s what you’ll learn;

  • How long tap water takes before it’s safe for fish
  • How long the water conditioner takes to work
  • Other ways to remove chlorine from water

Let’s begin.

How Long Does It Take For Tap Water To Be Safe For Fish

Before we discuss how long it takes for tap water to be safe for fish, we have to confirm whether it’s safe for fish in the first place?

After all, there are plenty of other choices.

You might get gallons of DI or RO water, pre-softened water, or even bottled water, which depending on the brand you are getting, might off-set your whole aquarium budget (though your fish might feel classy swimming in it, then they will start producing waste in it).

Fish don’t care about where the water comes from, as long as it’s healthy and has everything they need in their own little microhabitat in the tank, and doesn’t have chemicals and substances that might make them sick.

For most freshwater fish, tap water is safe after some treatment or waiting time. But for saltwater fish or fish that come from brackish water, you may need to “overhaul” your tap water or put something different in.

This is why; most people use tap water to fill up their tank. As for how long it takes before becoming safe for your delicate little friend, depends on two factors:

  1. Whether you are just letting water sit, OR
  2. You are using a conditioner to make the water safe for your fish.

Tap water comes loaded with Chlorine, which is put in there to kill germs and disinfect the water. It’s safe for humans to drink (as long as it’s less than 4 milligrams per liter or 4 PPM).

But even that concentration is bad news for the fish. They need Chlorine concentrations as low as three micrograms per liter or 0.003 PPM or lower would be required.

Even if it doesn’t kill your fish outright, a higher dose of Chlorine will stress them out or make them sick.

So the standard practice is to let the water sit in your clean tank for at least 24 hours (ideally 48 hours) to aerate.

Further Reading: Why wait 24 hours to put fish in a tank?

This ensures that many of the harmful chemicals in the water make it safe for us to drink completely evaporate.

Ensure that you don’t put a lid on the tank and, ideally, use a pump to move the water around. The more surface water comes into contact with air, the faster chemicals within it might evaporate.

But letting water sit in an aquarium for one to two days, while feasible when setting up the tank the first time, is difficult to do during water changes.

You can’t just check your fish into an aquarium hotel, and they may have to sit in a quarantine tank and stay there for a day or two until tap water in the primary tank is safe.

Hence, water conditioners;

Water conditioners are designed to neutralize the Chlorine in tap water and make it safe for your fish. They work significantly quicker than letting the tank sit out and offer a more practical water change solution.

How Long Does Water Conditioner Take To Work?

The first thing to ensure is that you use the conditioner’s right amount/dosage prescribed on the bottle/container.

Different conditioners might have different concentrations, i.e., one cap for ten gallons or one teaspoon or ten gallons.

It’s imperative because if you don’t use the conditioner’s right amount to treat your tank’s tap water, the time it takes for the conditioner to work won’t matter. Because you haven’t dissolved enough chemical in the water to neutralize all the Chlorine.

After you put in the water conditioner, it should take about 15 minutes to work. That’s the most conservative estimate and something most aquarists agree with.

In an already established tank (when you are doing a water change with tap water), you only need to let the water sit for 15 minutes before adding the fish.

Some people believe that with the proper flow (and active water pump), which moves water around to ensure that the conditioner is adequately spread around the tank and removing Chlorine from the whole tank, you can add fish after just about two to five minutes.

But if you have a larger tank and not enough circulation, you may need to wait 30 minutes before the tank is safe to put the fish in.

Also, it’s important to follow the directions that come with the water conditioner container.

However, that won’t be the case if you are using sodium thiosulfate – which is significantly cheaper than a conditioner.

But it also just neutralizes Chlorine and doesn’t condition your tank water in any other way.

How Long Does It Take For Chlorine To Evaporate From Water If You Let It Sit? 

That depends upon several factors: Chlorine’s initial concentration, aeration and surface area available for evaporation, whether you are running a pump or not, etc.

And even then, there are two answers;

It takes 24 to 48 hours for enough Chlorine to evaporate from water to make it safe for the fish if you just let it sit in the tank.

For most of the Chlorine to evaporate, the most common and quantifiable answer we found was 110 hours. That’s how long it takes for 2 PPM Chlorine to evaporate from 10 gallons of water.

And that’s when you don’t do anything special to it and just let it sit.

How Long Does Chlorine Stay In Water?

Most of the Chlorine typically evaporates from water within 24 to 48 days.

Though if we go by the 110-hour timeline and 2 PPM concentration, it might be safe to say that Chlorine stays in the water for 4 to 5 days.

Chlorine’s inclination to evaporate, leaving water behind, is why many water companies had to switch to chloramines, which is much stable and stays in the water.

Another stat to endorse this notion is that swimming pools, especially busy ones, dose their pools three times a week.

This reflects that Chlorine doesn’t stay active (and kill germs and bacteria) for more than two or three days at most. Other factors contribute, too, like how much sun the water is getting, the surface area, and how much water movement.

Does Water Softener Remove Chlorine?

A water softener serves a different purpose.

Its job is to remove calcium and magnesium from the tap water. And even though your fish doesn’t use soap (soft water ensures less soap is consumed), they may have certain water hardness requirements, depending on which natural habitat they come from.

But a water softener is not a “de-chlorinator,” i.e., it may not have the chemicals or compounds necessary to neutralize Chlorine.

A water conditioner, on the other hand, may serve both purposes.

Does Boiling Water Remove Chloramine?

While Chloramine is added to the tap water for the same purpose, i.e., disinfecting water and making it drinkable, it’s slightly different from Chlorine.

The main difference is that it produces significantly smaller disinfection by-products, chiefly Trihalomethane (THM) and Haloacetic Acids (HAA). Chloramine is also pretty stable and won’t just leave the tap water if you let it sit (as is the case with Chlorine).

Other than that, it’s almost the same. Especially to fish that would “sink” to death if the quantity of either Chlorine or Chloramine exceeds a certain level.

The problem with Chloramine is its stability and relatively inactive nature. Unlike Chlorine, it sits in your water and cannot be easily removed, even by boiling the water.

One of the sources we found from a water company that claimed you could remove chloramines from your water by slow boiling it for 20 minutes.

But that doesn’t mean you can remove enough of the compound to make the water livable for your fish. That time might be for masking the taste it creates or removing enough to make it usable for sensitive people.

Also, boiling 10-20 gallons or even larger tap water quantities to put it in your tank would be unfeasible and quite costly, and you may have to boil it for an hour to bring the Chloramine level down enough for your fish.

So the answer would be: Yes. Boiling water may remove Chloramine from tap water, but it’s not feasible to get rid of the compound for aquarists. Much better alternatives would be a catalytic carbon filter (installed at the source), a small RO system, or even chemicals that can neutralize Chloramine.

Does Boiling Water Remove Chlorine?

Yes. Unlike its stubborn cousin Chloramine, Chlorine is easier to get rid of. It’s volatile, so at higher temperatures, it starts evaporating quite rapidly.

The Chlorine might be gone for small quantities of water before you bring the water to a full boil. Even for larger volumes, the maximum threshold is 20 minutes.

The problem again is with the volume. Boiling too many gallons of water might consume too much energy. A cheaper, less time, and less resource-consuming solution would be chemical treatment.

More Ways To Remove Chlorine From Water

If you don’t want to go with the conventional boiling or letting it sit method (which the “lazy” tank water is happy to do), or the more practical way of adding a de-chlorinating substance/compound, there are other ways you can look into for removing Chlorine from water.

Use an Air Pump to Aerate Your Fish Tank

Aerating your fish tank is important, even if we discard its application of removing Chlorine from water.

Aeration means that you are finding ways to diffuse more oxygen in the water (i.e., adding more air to the water) by disturbing the water surface (it’s one of the ways, at least).

Shallow tanks with a large surface area are naturally much better aerated than deep narrow tanks with a low surface area.

Naturally, the gas exchange happens at the surface of the water tank.

Some gases (carbon dioxide and Chlorine) go out, while the oxygen comes in. The natural gas exchange “rate” is determined by several factors (temperature, surface area, etc.), and two of them are surface tension and water movement.

By disturbing/breaking the surface tension and ensuring water movement (from the bottom of the tank to the surface), regular pumps, filtration, and an air pump can expedite gas exchange.

Thus, Chlorine leaves water much faster.

Use A Carbon Filter

Carbon filters, or more specifically, activated carbon filters, effectively remove chlorine from tap water.

Many households already have carbon filters installed somewhere in their plumbing to remove Chlorine from tap water.

In aquarium filtration, activated carbon is part of chemical filtration. It uses adsorption and “soaks” up Chlorine from the tap water and keep your fish safe.

The best part is a carbon filter will also help you get rid of Chloramine.

Try Adding Ascorbic Acid

You might have heard adding vitamin C to your aquarium tank, and you might have thought that since your little fishy friends can’t eat oranges (even if a piranha can certainly peel it), it’s for them, i.e., a supplement.

But it’s actually for removing Chlorine;

Vitamin C or Ascorbic acid is excellent at neutralizing Chlorine. It’s a safe, natural additive that you can put in your tank to neutralize Chlorine.

The dosing is about 2.5 parts Ascorbic acid to neutralize 1 part chlorine. Ensure that your vitamin C tablet or additive that you want to put in your tank doesn’t contain something other than the Ascorbic Acid, which might be harmful to the fish.

Remove Chlorine From Water With Ultraviolet Light

UV is often used for the same purpose as Chlorine: Disinfecting the water.

However, another use of UV light is de-chlorination. At specific wavelengths, UV light instigates photochemical reactions.

These reactions can reduce the quantity of free Chlorine and chloramines in your tank water. Whether or not a normal UV sterilizer for your tank is powerful enough to reduce the amount of Chlorine is not clear.

You may have to contact your UV lamp/sterilizer supplier to confirm whether it’s capable of removing Chlorine from water or not.

While it’s not an easy answer, hopefully, you now have some options to remove chlorine from your tap water before you add your fish.

Take care.