The Best Way To Add Fish In Aquarium – Step By Step Guide

You don’t want an empty aquarium. You want to put in fish! When the aquarium is cycled there are some steps to make to add the fish safely.

As a whole, you should transport the fish carefully, let them acclimatize by putting the bag they are transported into the aquarium. Then you should move the fish into the aquarium without pouring in the water they were transported in.

Since moving fish to a new environment is very stressful for them, you need to be very careful when moving fish over to a new aquarium. In this article, I will go through every step thoroughly so you can do a safe implementation of your fish.

1. Plan your trip home from the store ahead

Everything starts before you even go to the store.

You need to have a plan for how you should transport your fish home from the store.

The fish will be put inside a bag filled with some of the water they were living inside at the store. This bag of water is just a bag, nothing else. No pump, no filter, no nothing.

This is very stressful for the fish, think about being put inside a bag yourself. It would be very claustrophobic. This is why you need to plan your trip so the fish doesn’t have to be in the bag for too long.

Also, when the fish are stressed the water gets very dirty. They will poop inside the bag and release stress hormones.

This is harmful to the fish.

A trip of 3-4 hours is possible for the fish but the shorter the better. If you have something else to do while getting fish, do it before getting the fish.

After 3-4 hours the oxygen will deplete. Some stores are offering oxygen during the transport if it is a long trip home.

You should also take into account of how the weather is.

The fish need a certain temperature depending on the fish. If the temperature is different, the fish will get more stressed.

The water that is put inside the fish bag is at a certain temperature suitable for the fish. If it’s hotter or colder outside, the temperature will change.

The best way to keep the temperature in the fish bag is to put the bag inside a thermal bag. This will keep the temperature.

I actually use a styrofoam container and it’s holding its temperature fine. I use a styrofoam box similar to this one which you could get on amazon.

If you are driving home, be sure to not have too hot nor too cold inside the car while traveling with the fish. Even if they are inside the styrofoam container, the fluctuations will be more and the fish will be more stressed.

If you travel by public transport, be sure to catch your ride. You don’t want to wait too long for the next ride with your new fish sitting in your box, being more and more stressed.

It could be better to catch a taxi if you need to go by public transport.

2. Do a small water change

When you get home, put the box with your fish aside, for now, because now you want to make sure the water inside your aquarium is welcoming to the fish that will have it as their new home.

The next step is to do a small water change. That is to be sure the water is clean and that the water parameters are fine inside the aquarium.

If you don’t know and need help with a water change, I have written an article about exactly how to do a water change here at Fish Keeping HQ.

While doing the water change, add some conditioner into the water.

Most of the conditioners have some anti-stress properties making the fish less likely to be more stressed when put inside the aquarium.

The water change should be around 10% of the aquarium size. It’s enough water to be changed and your new fish don’t have to wait too long for you to be done with your change before the next step.

3. Let the fish bag float in the aquarium for 15 minutes

When the water change is done, you should take the bag out from the transport container. But DON’T take the fish out from the fish bag yet!

Keep the fish inside the bag and put the bag itself into the aquarium. You could open the bag and hang it on the side of the aquarium, but with the water in the bag still at the same level as the water inside the aquarium.

You could also just dump it in the aquarium and let it float on the water surface.

My preferred method is to let it hang on the side of the aquarium since I feel I get more control over the bag.

Turn off the light, since the fish in the fish bag is stressed they will be a little more comfortable if they are not as visible. By turning the light off the other inhabitants in the aquarium will have a harder time seeing the new ones.

This will make the new fish a lot less stressed while being as exposed as they are, having nowhere to go.

Let the bag just sit there for about 15 minutes.

This is to slowly adjust the temperature in the fish bag to the same temperature as you have in your aquarium, It’s the start of the acclimatization process!

If you have fish inside your aquarium you will probably find that they are curious about what is happening. They will swim towards the bag and take a look at what’s inside. Even though the light is turned off.

This will also make the fish you already have to explore and see what their new roommates will be.

4. Pour a small amount of water into the fish bag

Now your bag has been floating inside your aquarium for about 15 minutes and the water inside the fish bag should be about the same temperature as the water inside your aquarium.

If you want, you could measure the temperature to be sure the temperature is roughly the same, but it’s not necessary. The bag will sit there for a little bit longer and the temperature will adjust a little bit more.

Now you want the new fish to get used to the water quality inside the aquarium.

This is because if there are big differences in the pH between your aquarium water and the water from the store. The fish will be more stressed and probably die.

To acclimatize the new fish to the potential new pH, you have to do it slowly.

You should pour a little bit of water from the aquarium into the bag. And I mean just a little bit! Don’t pour more than 0.5 cups (1 dl) into the bag.

Do it every 5 minuter 3 to 5 times.

You will be better off doing a little less water inside the bag and do it a little more times than doing a lot of water fewer times.

pH is one of the most important parameters to keep stable for the fish, so big fluctuations in pH are harmful. So, do this carefully!

5. Pour the fish with the water into a bucket carefully

Now you are done with the acclimatization of the new fish. They are now used to the water parameters and the temperature of your particular aquarium.

Now it’s time to move the fish from the fish bag into the aquarium.

But you don’t want to just pour them into the aquarium.

The water they have been transported in is very dirty from the stress the fish has been through the whole journey. You don’t want that dirty water inside your aquarium!

To get the fish inside your aquarium you could put your net inside the bag and take the fish out and put them into the aquarium.

That’s not the best solution to move the fish over because there is a risk of you harming the fish when putting a net inside such a confined container as the fish bag.

A better solution is to put the fish with the water from the bag into a different container. This will make it easier for you to pick the fishes up and it’s also reducing the risk of you contaminate your aquarium water.

The bigger container could be a bucket. Be sure to put some aquarium water inside though to be sure there is enough water for the fish to swim inside.

On my recommended tools page I have written about the Eheim multi-tool box which is perfect to use as a second container to put the fish in. That’s what I use and it works like a charm.

While having the fish and the dirty water inside the container, be sure to sieve out any debris from the water to lower the risk of you getting it inside your aquarium.

Just take it out with your net and throw it away. After that, you are ready for the next step!

6. Move the fish from the bucket into the aquarium

Now it’s time to put your new babies into their new home.

Take your net, and carefully lower it into the container where you have your fish. Be sure not to harm any of your fish with the edge of the net. Scoop up the fish inside your net and quickly move them over into the aquarium.

Don’t do it so quickly that you will harm your fish, just don’t keep the fish out of the water for too long since they are already stressed.

Once you have put your net containing fish into the water move the net in the opposite direction as you were while scooping the fish up.

This will make the net be inside out, helping the fish out from the net, into the aquarium.

Take a look that there is no fish stuck inside the net by moving the net a little bit inside the water in the aquarium.

Once you are sure all the fish got into the aquarium, redo the procedure if you have more fish inside your container until all the fish are inside the aquarium.

When you are done, throw the water inside your container away. This is the dirty water that you don’t want inside your aquarium.

Since you have taken out some water from the aquarium into your container, there is a risk of the water level being a little too low.

Top it up using your container with new, fresh, water, as if you would do a water change. Just be sure you rinse the container out for old, dirty water beforehand.

All this time, you have to keep the light off! When the new fish are implemented they will explore and try to find the hiding places inside the aquarium.

They will find the plants, roots, and rock to hide in rather quickly, but until then the light should be off.

If the light is turned on too quickly, the fish will get more stressed and in the worst case, the implementation could be a disaster.

The light should be turned off for about 1-2 hours, if possible you could add the new fish when the light is turned off. Then you don’t have to remember that you have to turn it on again.

7. Don’t feed your fish for three days

Now that you have added your fish, it’s not over just yet.

You have to make sure the quality of the water is optimal until the fish are getting used to their new environment.

If the water quality is bad, the fish will get stressed and die. Therefore you don’t want to feed your fish for three days. In fact, you should not feed the fish (if you have any) the same day you put your new fish in either.

That’s because you don’t just need to acclimatize the fish, but also the bacteria living inside the aquarium.

The fish you just put in are having bacteria from the fish store on them. Those bacteria could be competitors of the bacteria in your aquarium.

You have to let the bacteria inside the aquarium fight the new bacteria to get a balance in the bacteria flora inside the aquarium.

If you feed your fish too early your bacteria will not be able to break down the left-over food. This will harm the water quality.

The newly added fish are more prone to get infections since the stress that they have gone through is removing the protective coating on the gills.

If the water quality gets worse (which it will if the bacteria are not able to break down the rests) the newly added fish are more likely to get sick and die.

After about three days the bacteria should be in balance and the fish should be acclimatized to their new environment.

Generally, your fish will be fine without food for more than three days, so you should not worry about not feeding them for that period of time.

Now your fish should be fully acclimatized and the water balance should be fine too which makes the best possible environment for the new fish.

If you follow these steps, you reduce the stress of the fish making them less prone to get infections and you are more likely to have happy fish that are enjoying their new home!

Related Questions

Can you add fish to a new tank right away? As a whole, you should wait for the tank to cycle before putting in fish. That will take about 2 days with the pump on. Otherwise, you run the risk of getting ammonia or nitrite spikes which is lethal to fish.

How to know when my aquarium is ready for fish? To be sure your aquarium is done cycling, measure that the pH, KH, and nitrite levels are okay. When putting fish inside, don’t put in too many at once and monitor the water closely.

How do you help a stressed fish? The best way to help a stressed fish is to have a good water quality, have a lot of hiding places for the fish such as plants and roots.


I have been a fish keeper a big part of my life. During the years I have gathered and searched a lot of information about fish keeping and here, on the website, is where I share that information to help you with your fish keeping. I want to provide the information that I didn't get when I had a question about my fish tank.

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