Why Wait 24 Hours to Put Fish in Tank? (The Main Reasons)

why wait 24 hours to put fish in tank

Fish owners are always eager to put fish in new tank right after setting up a fish tank. But to keep your fish healthy in a new environment, there are some vital steps and rules that you need to carry on correctly, including the 24-hour rule.

Fishkeepers must wait at least a day before having any fish in a new tank.

But why wait 24 hours to put fish in tank? It is to ensure the nitrogen cycle is finished and to get rid of chlorine.

Let’s keep reading to gain a deeper understanding!

Why Do I Need to Wait 24 Hours to Put Fish in the Tank?


How long to wait to put new fish in the tank? You need to add fish after 24 hours because this is the required time for water to go through the nitrogen cycle and dechlorinate tap water.

Waiting for both steps to finish is completely crucial to preventing fish from getting sick and dying.

1. The nitrogen cycle

It’s very important to ensure the complete cycle tank before adding fish since the nitrogen cycle largely affects fish’s health. Nitrogen acts as a real hero that will protect fish from harmful waste by breaking down and turning the fish waste into nonharmful substances.

This process also helps beneficial bacteria to thrive.

Normally, the nitrogen cycle process of a new aquarium needs about three months to be completed, but now, you can speed up this process by buying bottled bacteria.

In this way, you can put a fish in the tank after 24 hours, that’s incredible!

You can find different bacteria bottle types with different kinds of bacteria, but it is advisable to buy dormant live bacteria.

It’s better not to order them online as these bacteria are so fragile. Remember the higher-quality products, the faster the nitrogen cycle gets done.

2. Dechlorination of water

What more? Water containing chlorine is completely harmful to fish, even if its concentration is lower than 0.2 ppm. Therefore, you need to get tap water in a vessel and leave it open for 24 – 48 hours to make sure the water is dechlorinated completely.

Tank Preparation


Moving fish into a new home can be particularly stressful, there are some steps you need to carry on to ensure your finned buddy feels comfortable in a new environment.

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  • Step 1: Consider the suitable size dimension for your fish. It’s best to start with a 10-gallon or 20-gallon fish if you plan to get small fish in small numbers. Go for larger ones if you want to keep a variety of fish of different sizes.
  • Step 2: Pick out the non-toxic fish tank decorative pieces, including rocks, gravel, and other safe toys.
  • Step 3: To ensure the tank water is safe for your fish, fill your tank with tap water and then add some chlorine elimination products and water conditioners.
  • Step 4: Before having your aquatic pet inside, connect the air pump to ensure the oxygen level in the fish tank. Having some live plants is also good for circulating oxygen.
  • Step 5: After pumping water, make sure it is flowing through the tank filter. This also encourages beneficial bacteria to develop strongly.
  • Step 6: The last step is to wait for the nitrogen cycle to complete, which will take 24 hours at least.


*Can you add fish to a new tank right away after conditioner? The answer is no. There are still other steps coming next, including testing the water and building up good bacteria.

Test the Water


Testing the tank water quality is one of the most vital factors before introducing fish in a new aquarium. This step ensures the water is 100% clean and safe for your fish, as untreated tap water is detrimental to the health of fish. You can implement these steps by using a water tester.

There are several water parameters you need to pay attention to when checking the water in the fish tank:

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  • Nitrites and nitrates, ammonia, and chlorine must drop to zero.
  • pH level should match or be close to the fish shop or where they’re coming from. Normally, an acceptance pH level is between 6.5 and 9.0


Each fish has its own requirements, so it’s important to know what your fish needs.

*How long after treating water can you add fish?

To know when your tank is ready for fish, you need to check the Nitrogen Cycle. This cycle is considered to finish when the ammonia is at 0, and the nitrate is below 40 ppm.

Remember, not only for a new tank setup, if you drain a fish tank for cleaning, you also need to wait 24-48 hours for parameters to stabilize before bringing the fish back.

If you keep some betta, 24 hours is the needed time to put betta fish in the tank after cleaning.

If you are a beginner, speaking to a fish expert is always recommended before acclimatizing any fish.

Give Beneficial Bacteria Time to Develop in the Fish Tank

Beneficial bacteria are helpful when it comes to removing ammonia buildup and breaking down waste products.

After treating the tank water, it is critical to let the water sit for at least 24 hours before adding the fish to make sure the accumulation of good bacteria builds up in the aquarium. To speed up this process, you can think of feeding the bacteria.

Frequently Asked Questions


What happens if I put a fish in the tank before 24 hours?

Suppose you hurry to put a fish in the tank before 24 hours when the nitrogen cycle is not finished. In that case, ammonia from the fish will be excreted, which will poison the fish.

So, 24 hours is the minimum time to run through the nitrogen cycle to give the good bacteria time to develop and dechlorinate water.

If these steps don’t get done in 24 hours, you may have to add fish after 48 hours. If not, your fish will be killed by respiratory problems and ammonia.

All of these problems are caused by untreated water and uncycled tanks.

How soon can I add fish to a new tank?

How soon you can add fish to your tank mostly depends on how fast you deal with untreated water, the nitrogen cycle, and how long beneficial bacteria can thrive.

24 hours is the minimum time to get all necessary steps done and to bring all the main water parameters, including ammonia, nitrates, temperature, or pH, to healthy levels for fish to live in.

So, to put your fish in a new tank as soon as possible, you need to find a way to progress all these steps quickly and remember to check the tank’s water parameters to ensure the tank is ready.


Why wait 24 hours to put fish in tank? It is highly advisable to let the water sit for at least 24 hours before putting fish in to get rid of all toxic elements like chlorine, finish the nitrogen cycle and stabilize important water parameters.

Fish are highly sensitive to their water environments. Therefore, you can’t risk losing all of them if you don’t take these preparation steps properly.