Skip to Content

How to Add Fish to a Freshwater Aquarium Safely! (Guide)

get 5 secrets to thriving plants

Whether you are setting up a new fish tank or trying to add new fish to an already established tank it is important to know how to add your fish safely.

This will ensure your fish do not get stressed during the process.

If adding fish to a new tank, let your tank cycle for at least three weeks to ensure good bacteria and the level of the parameters even out. When adding fish to the tank, let the bag loat for at least 10 minutes and gradually add water to it to have even water parameters.

There are also several other factors and steps involved in ensuring a smooth process for your fish. Keep reading to learn more about adding fish to your home aquarium. 

Adding Fish to a New Tank

Starting a new tank, whether it is your first tank or your third, can be very exciting! However, as exciting as it can be, you’ll want to make sure everything is done right to ensure your fish thrive and have a happy life.

Guppies acclimating

With some research and a little work, any tank can be successful, and leave you with less stress!


To add fish to a new tank there are a few steps you will have to take before adding any fish to the tank.

First, you will want to make sure you have the appropriate equipment for your tank, starting with the basics like a lid, a heater, and a good filtration system.

Once all of your equipment is set up in your tank you will need to start filling the tank with water that you have mixed the starter conditioner with. This will de-chlorinate the water that you are adding to the tank. After this, you must allow at least three weeks before adding in fish.

Letting your tank cycle is very critical as this will allow the water to cycle through the filters a few times.

This is important as this allows the water to be filtered out of any unwanted chemicals out of the water. This also allows time for beneficial bacteria to grow that will keep your water parameters healthy for your new fish.

Water Parameters

You’ll want to research what kind of fish you will want to place in your tank so that you have the water parameters set before adding the fish to the tank.

It is also best to not add too many fish at one time. It is also best to add a few to start and slowly add more in.

This allows your filter to keep up with the rise in waste it will need to filter out of the water to ensure ammonia and nitrite levels do not rise.

Slowly Add Fish to Tank

Once you bring your new fish home it is best to leave them in their bag at the surface of the tank.

This will help acclimate your new fish to their new surroundings. Leave them at the surface for about 10 to 20 minutes. This will even out the water temperature.

Apart from the temperature, it’s also important to check the other water parameters such as pH. The safest way to prevent a shock is to gradually add aquarium water to the bag. 

After an hour or so of acclimating and adding water, you can add the fish.

It is normal for fish to hide when they are first added. This is because they can be stressed from the move, as well as the new environment completely.

This is when you want to ensure you placed ample hiding spots in the tank for them to hide in to feel safe.

It may also be a good idea to leave their light off for the first few days as they hide. This will help the more shy ones feel safer as they acclimate.

Also, feed them sparingly until the water has gone through a full cycle with the new fish.

Acclimating Fish to an Established Tank

Adding new fish to a tank that is already established can be difficult if you do not take the proper steps to ensure to do this safely. 

This is something that should be done slowly, do not rush, and may be best to only add new fish one at a time to avoid problems.

Too many fish at once can cause a disturbance and stress in the fish you’ve had prior. 

Before adding any new fish to an established tank you will want to make sure everything is clean and the parameters are right where they need to be.

The last thing you want to do is add a new fish into a new community, which can be stressful, and have a dirty unstable environment.

The first step you will want to do is to make sure the tank requirements for the new fish match what you have already.

If their tank requirements are not compatible with what your existing fish need then you may want to start another tank entirely.

You may want to dim the lights in the tank as the first step to try and reduce stress moving forward. As with adding fish to a new tank you will want to leave them in their bag at the surface of the water. 

This allows them to start adjusting before being thrown into a new home. After they have been floating around for ten minutes add a cup of the tank water into their bag. Continuing doing this every ten minutes until their bag is full. 

After their bag is full give them another ten minutes, then carefully scoop them out with a net and add them into the tank, you’ll want to avoid the bag water spilling into your tank to ensure your water parameters.

Some find it helpful to add the new fish in while you are feeding the rest of your fish. 

This provides a distraction as your new fish enters the tank and may want to find a place to hide. This will also fill your existing fish up and they will tend to be less aggressive toward the new addition to your tank. 

You will also want to leave that light off or dimmed for a few hours after adding the new ones to the tank.

This creates a less stressful environment for not only the new fish but your existing fish as well. Giving your fish time to acclimate slowly is key to not put too much stress on your fish.

Ensure You Add Proper Tankmates 

Even though there are very important steps in adding fish to a tank whether it be a new tank or one that is already established with a community, the most important thing is making sure the fish you are adding are compatible with each other. Compatibility is key!

You will want to ensure that the fish not only require the same water and tank conditions but need to be able to coexist together safely.

Some fish just don’t mix well with others. This could be because some are more aggressive than others, or some may see other species as food.

When starting a community tank you will need to research each species you are interested in. There are many combinations of community tanks that you can acquire.

Bad tank mates can cause a lot of stress in the tank, can lead to injuries in your other tank mates, and can result in death as well.

For example, some cichlids are a bit larger and aggressive than other fish. You would never want to add them to a tank mostly inhabiting small fish such as tetras and guppies.