Why You Have To Wait 24 Hours To Put Fish in Tank

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by Jason Matthews



As avid fish owners, we understand the eagerness around wanting to bring fish home as soon as you decide to set up a tank. But you may have heard talk about waiting 24 hours before putting fish into a new aquarium, and we’re here to tell you that this is an important step.

You should wait 24 hours to put fish in a new tank because it gives the water time to run through the nitrogen cycle and eliminates chlorine. Ignoring one or both of these vital steps could kill your fish.

We’ll teach you why the nitrogen cycle is so important, how chlorine evaporates in 24 hours, and tips for setting up a fish-friendly water environment.

Understanding the Nitrogen Cycle

nitrogen cycle

The nitrogen cycle is crucial to a fish’s health, as it encourages good bacteria to bloom and thrive. Nitrogen is essential to sustaining life, as it works to break down the wastes your fish eliminate before they turn into toxins that can kill them.

Traditionally, it can take up to three months for a new tank to complete the nitrogen cycle process so that it’s fully thriving. During this set-up time, aquarium owners place plants and hardy fish in the tank to spark the start of the nitrogen cycle.

But you don’t have to wait three months before putting fish into your new tank. Instead, pet stores sell bottled bacteria that’ll make your tank ready to receive fish in only 24 hours.

Using 24-Hour Bottled Bacteria

Many types of bottled bacteria exist on the market. We recommend selecting live bacteria that are in a dormant state.

Since these good bacteria are so fragile, purchasing them at a store is best instead of ordering them online. Furthermore, this isn’t the time to get cheap on your fish; the higher-quality products will have a better chance of sparking a faster nitrogen cycle.

While many bottled bacteria packages tout being fish-ready in 24 hours, it’s never a bad idea to wait a day or two longer.

Furthermore, always test the water parameters before adding your fish to the tank. We’ll talk more about this shortly.

Waiting 24 Hours for Chlorine

testing tap water for Chlorine

Most tap water contains chlorine, which is deadly for fish. If there’s a chlorine concentration of as little as 0.2 to 0.3 parts per million (ppm) in the tank, you can expect your fish to die quickly.

In contrast, chlorine concentrations less than 0.2 ppm are still toxic to fish. However, they’ll die slower, as the chlorine will damage their gills.

The good news is that chlorine is fast at leaving water and escaping into the atmosphere. Therefore, leaving tap water in an open container for 24 hours is an excellent way to ensure that you fill your fish’s tank with chlorine-free water.

Alternatively, you can purchase a chemical to eliminate chlorine from the water faster. Regardless of the chlorine elimination method you use, it’s crucial to test the water for chlorine before introducing fish into their new tank.

Testing Your Tank’s Water Parameters

Twenty-four hours is the minimum time you should wait to put fish in a tank with new water. But waiting for the 24-hour mark to pass isn’t enough; you should also check the tank’s water parameters to ensure the water is suitable for sustaining fish life.

The most important water parameters to check include:

  • Temperature
  • Ammonia
  • Chlorine
  • Nitrite
  • Nitrate
  • pH

In all cases, the chlorine, ammonia, and nitrite levels should be zero. Nitrate levels should be under 50 ppm.

The numbers for the temperature, ammonia, and pH vary according to the types of fish you’ll be adding to the tank. Most fish can tolerate a range for each of these parameters, with some fish having a higher tolerance for a larger range than others.

So, once you set up your fish tank with water and the 24-hour period passes, check the water’s status. Many pet stores sell testing kits that test for all of the items we listed except temperature.

In addition, purchasing an aquarium thermometer and keeping it in your tank 24/7 is ideal for ensuring it stays within your fish’s preferred range.

The Aquarium Filter’s Role

All fish tanks should have a filter, as they help manage the amount of ammonium, nitrite, and nitrate that remains in the water—an especially crucial factor after 24 hours pass and you add fish to your tank.

There are three different kinds of filters you can use:

  • Mechanical 
  • Chemical
  • Biological

Biological filters are particularly interesting for what we’re talking about, given that they contain live, healthy bacteria. All fish tanks should have a biological filter, as they help break down the toxins of ammonia and nitrite.

So, in addition to adding 24-hour bottled bacteria to dechlorinated water, it’s helpful to set up your filtration system. A biological filter will support your efforts to infuse your fish’s water with healthy bacteria to help them thrive.

Using Resilient Fish

Platys fish resilient

Despite using a 24-hour bacteria product and ensuring your tank is chlorine-free, starting a new tank with resilient fish is still a good idea.

Examples of hardy fish that are ideal for new tanks include:

  • Platys
  • Mollies
  • Barbs
  • Danios

The good news is that these fish are also inexpensive. You don’t need very many fish to improve the nitrogen cycle and ensure that everything is running smoothly.

After you’re confident that your initial resilient fish are happy with the water in their tank, it’s safe to start adding more fragile species.

The Bottom Line

All fish tanks require a minimum of 24 hours to eliminate chlorine and kickstart the nitrogen cycle, as long as you use a bottled bacteria booster. If you’re not using a booster, it can take months to ensure your tank’s water is suitable to receive fragile fish.

So, hold yourself back from running to the pet store to pick out your fish. Preparing your tank first is crucial, and you can work on arranging the aquarium’s decor while you’re waiting for the water to meet your fish’s parameter needs.


Jason Matthews

My name is Jason Matthews, and welcome to my website. When other kids were bragging about how their dog could sit and roll over, I was bragging about my latest Betta Fish and the cool sea castle I just added to his aquarium. 

Jason aquariume

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