Hepper is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no cost to you. Learn more.

How Long To Let Fish Acclimate To New Tank – Tips & Tricks

Lindsey Stanton Profile Picture

By Lindsey Stanton

acclimatize fish in bag tank

Fish cannot just be dumped into a new aquarium and expected to be happy, let alone to survive. One of the most important things to do when buying a new fish is to let it acclimate to its new habitat.

How long to let fish acclimate to a new tank is a hot-button topic in the fish-keeping world. Let’s get to the bottom of this issue and find out how long it takes for fish to acclimate to a new tank.

clownfish divider2 ah

How Long Does It Take for Fish to Acclimate to a New Tank?

goldfish in plastic bag
Image Credit: Payless Images, Shutterstock

One of the most common misconceptions and false pieces of advice given by amateurs is that it only takes around 15 minutes for fish to acclimate to a new tank. They will tell you to float the bag of water with the fish in it in the tank until the water reaches the same temperature inside of the bag as in the tank.

Yes, this is partially true, but there are a couple more steps involved and it certainly takes more than 15 minutes. Ideally, you should take at least one whole hour to let your new fish acclimate to their new environment. This can take even longer for larger fish.

Acclimating Your Fish – Step By Step

The best thing we can do for you here is to provide you with a step-by-step guide on acclimating your fish to its new home, so let’s do that right now.

  • When you buy your new fish, get it home as soon as possible. Don’t dilly dally or go shopping in between. GO right from the pet store to your home. The water in a plastic bag is not ideal for long-term living, it doesn’t have much oxygen, and fish don’t like being in plastic bags.
  • Rinse the exterior of the bag off.
  • Pour out the excess water in the bag, but leave enough to cover the dorsal fin.
  • Place the bag into the aquarium. Keep the bag open and leave it folded back at the top so it can float in the aquarium without sinking, and so that oxygen can get to your fish.
  • After 10 minutes of the bag floating in the water, add some of the aquarium water into the bag. You should be tripling the volume of water in the bag within an hour, using only aquarium water to do this.
  • You should add a little more water from the aquarium to the bag about every 5 minutes. Do this for about an hour and the temperature inside of the bag should be the same as the water temperature in the aquarium.
  • Once you have done this, you can introduce the fish into the aquarium without the bag.

Why Acclimate Your Fish?

Several important things come along with the acclimating process. As we said, you can’t just dump the fish into the water. Up above, our main concern was the temperature, but there are other factors at play here as well.

  • All fish need certain water parameters. Of course, all fish are different, so you do need to make sure that the aquarium you have contains the proper water for the fish. If you already have other fish in the tank, you need to make sure that both fish can survive in the same water.
  • Slowly adding water into the bag not only helps with temperature, but also helps the new fish slowly get used to the water’s acidity level (pH), hardness, and the number of other compounds in the water. You should ideally have the tank at the proper parameters before inserting the fish.
  • Fish are not always friendly and if you have a pre-existing community, they might not be happy about a new fish which they will perceive as an intruder. Putting them in the aquarium in the bag will give the fish a chance to get used to each other, and worst comes to worst, at least there is a barrier in between them.
  • Fish are also not a huge fan of noise. Filters and waterfalls can be a little disturbing to them. The plastic bag will provide a bit of a sound barrier. It will provide enough of a barrier to muffle a good deal of sound, but lets enough sound through to slowly get your fish used to the new sounds.
fish in bag
Image Credit: kao, Shutterstock

aquarium plant divider

Tips For A Stressed Fish In New Tank

Keep It Alone For A While

If you have a fish that is stressed out in its new tank, it may be wise to keep it alone for a while. It may be the tank mates which are stressing it out.

If this is not possible, you can consider getting a tank divider to create a safe space for the stressed fish.

Wait, Be Patient

Stressed fish just need some time to acclimatize, so sometimes the best solution is to simply wait for a few days, or even a few weeks, and give it some space.

Remember, it is also getting used to you, so don’t tap on the glass or interact with it too much. Just let your new fish settle for a while.

Fish Requirements

Always ensure that your tank meets the specific requirements of the new fish you have gotten.

This means the proper lights, the proper water temperature, and water parameters, as well as the proper substrate and plants for it.


divider fish plants 2

Commonly Asked Questions

How long Do You Leave Fish In Bag Before Putting In Tank?

You don’t want to leave your fish in a plastic bag for very long. Inside of a normal plastic bag, oxygen will run out in between 1 and 2 hours, so there is that to keep in mind.

You want to put the bag with the fish, in the aquarium right when you get home. This way, the water in the bag will slowly reach the temperature of the water in the tank.

This should take no more than 30 minutes, at which point it is OK to allow the fish into the tank (more on transporting a fish safely here).

Can You Put Fish In A New Tank The Same Day?

Yes, absolutely can you put a new fish in a new tank on the same day, and in fact, it is something you should do.

As mentioned before, you cannot leave a fish in a bag for very long, so you have no other option than to put it in a new tank the same day.

If you are worried about the fish not getting along with each other, you can try using a divider to give your new fish some space.

How Long Do Fish Need To Acclimate?

It is going to take a fish about 15 minutes to properly acclimate to a new tank. Remember that this has to do with the water temperature.

It is going to take between 15 and 30 minutes for the water in the bag to reach the temperature of the new tank’s water temperature, which is pretty much the whole acclimatization process.

How Many Fish Can Be Added To A Tank At Once?

What you need to know here is that adding too many fish to a tank at once can cause the water chemistry to change, quite drastically.

Adding too many fish can cause the nitrogen cycle to stall, which is very bad. The rule here is that you never want to add more than 3 fish to a tank at the same time until the nitrogen cycle has been completed and a new cycle has started.

Keep in mind that depending on your aquarium, the nitrogen cycle can take between 2 to 6 weeks to complete and start again.

How Long Do Fish Need To Adjust To Water?

There is no good answer to this. In theory, as mentioned above, it takes 15 to 30 minutes for a fish to adjust to the water.

However, how long it takes a fish to adjust to a new aquarium as a whole depends on the fish itself, as well as the setting.

colorful cichlids swimming in tank
Image By: andreibucataru.ro, Shutterstock

wave divider


Remember folks, never just dump a new fish directly into the tank. This can create a lot of stress for your new fish and the old ones too. If you don’t go through a proper acclimatization process, you may end up killing your new pet, so please be careful, be patient, and follow the steps we have outlined above.

See Also: How Long Can Fish Live In a Bag?

Feature Image Credit: Anze Furlan, Shutterstock

Related Articles

Further Reading

Vet Articles

Latest Vet Answers

The latest veterinarians' answers to questions from our database