Do You Have to Let Water Sit Before Adding Fish? (And How Long)

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As an aquarist, I consistently heard that I should let the water sit for a while before adding my fish. Some people told me the water should wait 24 hours, while others argued it takes several days. Luckily, as the years passed, I gained some experience in this topic.

It is highly recommended to let the water sit for 24 hours before adding fish. That will allow toxic elements like chlorine to evaporate and stabilize the water’s pH by reducing carbon dioxide. Water conditioners may hasten the process and prepare the water for fish within 15 minutes.

As we proceed, I will discuss whether aging the water is actually necessary and what would be the best way to do so. That includes using water conditioners, such as the API TAP Water Conditioner (link to Amazon), to hasten the process.

Is it Necessary to Let Water Sit Before Adding Fish?

The technical answer is ‘Yes’. It would be best if you allowed water to sit before adding fish. Practically speaking, though, it depends on various factors, including the source of the water and the resources you have at your disposal.

Every new tank must be cycled before you can use it. The process can take anywhere between four and six weeks. The goal is to introduce helpful bacteria that can convert ammonia into nitrates and nitrites.

The water in a tank that has been cycled to completion should be safe for your fish, especially if you have taken the time to test its parameters. The same cannot be said for any new water you want to add to a tank during a water change or as a means of raising the water level.

Many aquarists will leave this water to sit for several hours or days because of the benefits associated with the practice, including:

1. Chlorine Reduction

Tap water is normally treated with chlorine. The chemical makes the water safe for human consumption. Unfortunately, fish hate chlorine. It might even kill them. But if you allow water to sit for several hours, the chlorine will evaporate, making the water safe for fish.

This is one of the primary advantages of this practice. However, it is also one of the key disadvantages. Many aquarists age water (allowing it to sit for several hours and days) because they don’t want to use de-chlorinators.

They want to eliminate chlorine using organic means. Unfortunately for these aquarists, aging doesn’t work on chloramine.[1] Chloramine is a combination of chlorine and ammonia. The authorities in certain regions use it to treat water because it is more stable.

You cannot remove chloramine by allowing the water to sit. Aging only works in situations where your tap water contains chlorine. Talk to your water supplier before you act. Ask for a report detailing the makeup of your tap water. You can use this information to determine whether you will age your water or treat it chemically.

2. Enabling Water Stability

Tap water is unstable. Because your suppliers apply pressure to the water when they deliver it to your home, it has several dissolved gasses that can affect its chemistry. Carbon dioxide is one of the most prominent. It can lower the pH. However, this change is temporary. 

The pH will eventually rise as the carbon dioxide levels fall. That sounds like a good thing. However, fish want stability. They react negatively to changes in temperature and pH. Aging the water enables the pH and temperature to stabilize, preventing distressing alterations to the tank’s chemistry.[2]

3. Cost and Accessibility

This practice is cheap. You can treat your water using chemicals. The right conditioners will not only eliminate toxins and heavy metals, but you can use them to apply a stress coat that has a soothing effect on fish.[3]

But you have to buy these chemical treatments before you can use them. This isn’t just a financial issue. Some people do not have any fish stores in their vicinity. They have to travel long distances to find aquarium supplies. 

While you can find decent aquarium conditioners on the internet these days, some people do not have internet access. For such individuals, it is not only cheaper but easier to condition aquarium water by allowing it to sit.

Does Aging Always Work?

No, aging doesn’t always work. You already know that it cannot remove chloramine. However, you might not realize that you cannot remove heavy metals either, not by allowing the water to sit, especially if the water has a lot of minerals. You require chemical solutions.

Is Aging Always Necessary?

It depends on the source of your water. Tap water should be allowed to sit before you add it to an aquarium because it has chlorine. Bottled water is less of an issue. You don’t have to dechlorinate it.[4]

However, bottled water is expensive. Most people cannot afford to buy bottled water in quantities that can fill their aquarium. You are also expected to check parameters like the pH and hardness because they may vary drastically from the range your fish want.

A third alternative is Reverse Osmosis water. RO water undergoes processes that remove all chemicals, toxins, and metals. RO water sounds attractive because you don’t have to leave it to sit to remove chlorine.

It doesn’t have chlorine, to begin with. However, because it is entirely pure, it lacks minerals like calcium that certain aquarium creatures require. RO water is also known for having unstable pH and hardness.

You can use conditioners to give RO water the minerals your aquatic creatures need. You can also use these to stabilize the pH and hardness, preventing sudden changes. 

How Long do You Let Water Sit Before Putting Fish in?

It is best to let the water sit for at least 24 hours. However, once you apply de-chlorinators and ammonia neutralizers, your tank should be ready to receive your fish within 15 minutes. The quantity of the water matters. The more water you have to age, the longer you have to let the water sit.

But as was already mentioned, the time you’ll wait won’t impact the chloramine levels. To reduce that, I suggest getting the API TAP Water Conditioner (link to Amazon). A few drops of that product will take care of everything.

How to Properly Age Aquarium Water?

All you have to do to age water is to leave it sitting in a container for several hours, possibly even days. But that isn’t always enough to produce the results you want. Many aquarists use the following methods to either enhance the efficacy of the aging process or to expedite it:[5]

1. Create Aeration

Add an air stone to the water. The improved aeration will elevate the rate at which chlorine and other dissolved gasses evaporate. For that purpose, I personally use the Hygger Aquarium Air Stone Kit (link to Amazon).

Some people use aquariums to age their water. In such cases, you can use filters and powerheads to expedite the aging process. Filters and powerheads agitate the water, allowing the dissolved gasses to evaporate at a faster rate. You can remove in a night what would typically take days to eliminate.

2. Use Ascorbic Acid

When you sprinkle ascorbic acid on the water, it will pull the chlorine and chloramine to the surface. Ascorbic acid is cheap and easy to use. It treats the water without affecting the oxygen levels.

3. Boil the Water

If you don’t want to wait for hours and days for the chlorine to evaporate, boil the water. This process produces results in just a few minutes. Many aquarists choose to boil their aquarium water because it can remove chloramine as well as chlorine.

4. Use UV Light

UV light removes chlorine and chloramine safely and effectively. It also kills bacteria that cause diseases in fish. However, ascorbic acid and boiling are more convenient alternatives because UV filtration systems are pretty expensive. But if you have the money, UV light is a powerful tool for treating aquarium water.

Can You Chemically Age Aquarium Water?

Yes, you can use chemical products to age water. That usually involves water conditioners that neutralize chlorine, chloramine, and heavy metals. The approach has several advantages, including:

  • Time-Efficient

Chemical products are quick. You don’t have to wait for hours or days to dechlorinate your water. You can add fish to your tank within minutes. Also, you don’t have to wait until the boiled water cools down if you chose the boiling method.

  • Accuracy

The problem with leaving water to sit is that it involves a lot of uncertainty. No one can tell you for sure how long it will take to remove the chlorine. You have to test the water repeatedly. This is why aquarists are told to age their water for at least 24 hours.

It could take 48 hours or even longer for the chlorine to evaporate. Water conditioners are far more accurate. Their packaging has instructions that will tell you the exact number of drops you need to apply to treat a certain amount of water.

  • Efficacy

There is a limit to what the natural aging process can do. It can remove chlorine but not chloramine or heavy metals. Water conditioners do not have such limitations. They can remove ammonia, algae, heavy metals, and phosphate.[6]

They can also promote the growth of beneficial bacteria and remove the dirt and debris that makes the water cloudy. Chemical products are pretty comprehensive in their operations. You can use them to adjust the parameters of your water to suit the needs of your fish. 

As was mentioned above, conditioners can even apply a stress coat that can soothe fish. That includes the well-known API Stress Coat Water Conditioner (link to Amazon). This product would take care of your fish if their preexisting coat was damaged.

  • No Side Effects

For the most part, chemical conditioners are safe. Some people gravitate towards the natural aging process because they are convinced that chemical conditioners are a danger to their fish and the environment in their tank.

However, that isn’t the case. Aquarium conditioners are perfectly safe. You can even use more than the prescribed quantity without inflicting any significant side effects on your fish.

  • Quantity

With the natural aging process, you can only age small quantities of water at a time. Some aquarists solve this problem by keeping large reservoirs of aged water that they can use whenever they perform a water change.

But this isn’t an issue where chemicals are concerned. A potent conditioner can treat a large aquarium of water in one go, removing toxins and heavy metals within minutes. It should be noted that you don’t have to choose between these two methods. 

You can use them both. Start by leaving the water to sit for 24 hours. Then, add a conditioner to remove chloramine and ammonia. These two methods can complement one another. You don’t have to restrict your aquarium to just one of them.

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Generally, it would help if you let the water sit for about 24 hours before adding your fish. That will take care of the chloramine and carbon dioxide, which could be problematic for fish. To hasten that proceed, you may alternatively use water conditioners.

Another option is to boil the water. Then, once the water cools down and reaches a suitable temperature, you may add your fish immediately. Bear in mind that high volumes may require a bit more time. If you wish to stay on the safe side, let your water sit for 48 hours.