How Long Does Water Conditioner Take To Work?

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If you’re adding water conditioner to tap water to make it safe for your fish, the conditioner is ready to be added to your tank right away. It then takes roughly 24 hours after being added before all the water in the tank has been conditioned.

That’s the short version – read on to find out all about the process of adding water conditioner!

What is water conditioner?

Water conditioner describes any solution that optimizes the chemical makeup of tap water. In fishkeeping this usually refers to dechlorinators which make tap water safe for fish by neutralizing chlorine, chloramine and dissolved metals.

Other types of water conditioner include solutions designed to raise or lower pH, or to neutralize ammonia. For example, my Betta tank regularly experiences low pH, so I dose the tank infrequently with API’s pH Up! product.

Some of the water conditoners I have in my collection!

Do water conditioners work instantly?

Water conditioners generally take no longer than a few minutes to make water safe for fish. If you’re filling a bucket and you start by adding conditioner, it will usually have worked by the time the bucket has been filled enough to be ready to be added to your tank.

People often ask, ‘how long should I wait after I put a water conditioner in water to add it to my tank?’ Some water conditioners state that they take up to 5 minutes to work. In this case, rather than adding them directly to the tank, always mix them with the tap water and wait a few minutes to be safe.

My water conditioner of choice is Seachem Prime, which states on the bottle that it’s ‘better if added to new water first’. Although it does say it’s technically safe to be added directly to the tank, this seems like an unnecessary risk.

Once the tap water and conditioner mix has been added to the tank, it takes around 24 hours to fully cycle around the aquarium and mix with the existing tank water. This makes it pointless to perform water changes more frequently than once a day.

Do all fish tanks need water conditioner?

In very rare conditions, some tap water won’t need water conditioner. The majority of the time, however, tap water will contain chlorine which is used to disinfect the water systems in most cities and is toxic to fish, so you’ll need to neutralize it with water conditioner.

Besides this, there are other advantages to using water conditioner. Products like Seachem Prime can’t remove harmful chemicals and dissolved metals, but it can detoxify them by providing a tolerable chemical balance for your fish.

Products like Prime not only detoxify chlorine and chloramine, but ammonia, nitrites and nitrates, too.

When should you use a water conditioner?

Whenever you’re adding water to your tank, you should be using a water conditioner to make the tap water safe for your fish. This includes during your routine water changes and when you’re adding water to top up your tank if water has evaporated.

There’s no hard and fast rule for how often water conditioner should be used, so just follow your normal water change schedule or top off whenever the water level gets low.

I change the water in my tanks weekly, changing 10-20% of the water if the levels are normal. On the rare occasion that ammonia, nitrites or nitrates spike, I’ll increase the frequency and volume of the water change.

The reason for the increase in volume is to make sure I’m removing more of the ‘harmful’ water. During an ammonia spike, for example, changing 10% of the water only removes 10% of the ammonia. You’d be doing daily water changes for weeks to eliminate the problem.

Read more: How many water changes does it take to get rid of ammonia?

Get into the habit of using a water conditioner each time you add tap water to your tank to make sure you’re not risking the health of your fish.

Can I add water conditioner while the fish are in the tank?

If you’re doing a regular water change of 10-20%, you can safely add water conditioner while your fish are still in the tank. If you’re performing a large or complete water change, you’ll need to put the fish in another tank that’s cycled and contains conditioned water first.

Assuming you’re doing a small water change, the best advice is to mix the conditioner with tap water first, instead of adding tap water directly and then adding conditioner afterwards.

This is so the water conditioner has a few minutes to neutralize the harmful chemicals in the tap water before your fish are exposed to them, however short a time this may be.

The other risk of adding the conditioner directly to the tank is that you’re creating a high concentration of one chemical in a small area of the tank. Any fish swimming through this area are being exposed to a chemical rather than the optimal tank water they’re used to. This might distress or harm your fish.

Top tip: try to add the conditioned water directly into your filter flow so the new water is quickly dispersed into the tank rather than creating a hotspot of new water that contains all the newly added chemicals.

Can you use too much water conditioner?

It’s possible to overdose your aquarium with water conditioner if you add more than the recommended dose. Some fish are sensitive to changes in water parameters and can become ill or even die if you add too much of any chemical, including water conditioner.

Water conditioner binds to the oxygen molecules in the water where there is no chlorine left, making it hard for the fish to breathe. Manufacturers state you can add extra if you have high levels of harmful chemicals in your tank, but this should be a last resort.

Seachem Prime states on the bottle that ‘For exceptionally high chloramine concentrations, a double dose may be used’. It also says that ‘To detoxify nitrite in an emergency, up to 5 times normal dose may be used.’

However, adding more than a small amount of conditioner is a risk. This should only be done when the health of your fish is at risk and extreme steps need to be taken to save them.


Does water conditioner remove ammonia?

Water conditioners neutralize ammonia by binding to the molecules. This renders it safe, or by converting it to ammonium which is harmless to fish. This isn’t technically the same as ‘removing’ ammonia but the outcome is the same!

Does water conditioner lower nitrates?

Water conditioners lower levels of nitrate in fish tanks either by converting it to nitrogen gas, or by binding to the nitrate molecules, rendering them harmless.

According to, this makes it ‘possible for the bacteria in your biological filter to destroy’ the nitrate molecules, lowering overall nitrate levels in the tank.

Does water conditioner remove nitrites?

Water conditioners bind to the nitrite molecules in your aquarium. This allows the bacteria in your filter to convert them to nitrate. So the nitrites are not technically removed, just converted to a different chemical.


Most water conditioners mix instantly or are safe to add to your tank after a few minutes of being added to tap water. 

Once added to your tank with the tap water, the water conditioner takes around 24 hours to fully cycle through your aquarium and detoxify any harmful chemicals.

Always be sure to use the correct dose as advised on the bottle. Too much water conditioner can be harmful to your fish.

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