How to Introduce a New Fish to Your Aquarium


So, you’ve just picked up a brand-new angelfish from the pet store and are excited to it to your fish tank at home – we don’t blame you. Adding new fish is always exciting.

However, before you go dumping your new fish in, you should make sure that you’ve introduced it to the tank in the correct fashion. If you aren’t sure how, exactly, to add your new fish, we’ve got you covered.

Here’s a step by step guide on how to add new fish to aquariums as well as some useful information about the process.

The Acclimation and Transfer Process: Step by Step

For a stress-free, happy introduction, follow these steps when introducing new fish to your tank.

Introducing new aquarium fish

Test the Water

Before you add your fish to your tank, make sure all is well by checking the tank’s ammonia, pH, and chlorine levels. Chlorine and ammonia should be reading at 0, which is considered to be safe.

You’ll also need to verify that the water temperature of your tank is suitable for the new inhabitant.

If your ammonia or chlorine levels read anything other than 0, you’ll need to add a dose of water dechlorinating and/or ammonia binders to bring the levels down to 0.

Dim the Lights

Next, turn off any aquarium lights that you have on – yes, even the fantastic disco-ball lights you have going all day every day. This is done to reduce the stress on the new fish. If you can, you might also opt to dim the lights in the room that the tank is in.

Don’t worry, you can turn the lights back on later. There’s no need to worry about the appearance of your fish if you use your lights to enhance fish colors; a few hours won’t impact the process.

Float the Fish

Okay, when we say “float the fish” we don’t mean that you should dump the fish in and hope it floats. Nope, we mean that you should take the sealed bag containing your fish and float it in the top of your aquarium.

When you place your bag to float, be sure that it is far enough away from the aquarium heater that it won’t touch it; this could cause the plastic bag to melt.

Betta fish in pet store

Allow the bag to float for 15-20 minutes. This will allow the water temperature inside the bag to change so it matches the water inside the aquarium. Failing to match water temperatures can stress out your fish unnecessarily, as their systems are shocked by the temperature change.

Carefully Open the Bag

After you’re happy with how long your fish has been floating, carefully open the top of the bag without letting any water out.

Fold the end of the bag to create a hem-like air pocket that allows the bag to float upright. You may need to fold the hem once more.

Test the pH

Now, test the pH inside both the bag and the aquarium. Compare the results and take note of the difference.

As an example, if the water inside the bag reads at 7.0 and the tank reads at 7.2, the difference will be 0.2.

Transfer Water

Using a ½-cup measuring cup, dip it into the tank and pour one cup full of water into the bag with the fish. Wait 15 minutes before repeating the process as many times as necessary to get the pH levels of the tank and bag to match.

Based on a difference of 0.1 to 0.3, you should be adding ½ cup of tank water every 15 minutes for roughly an hour. A pH difference of 0.4 or more will usually require a ½ cup addition every 15 minutes for two hours.

Be sure to check the pH levels carefully before deciding on if it’s time to add the fish or not – even if it has been two hours.

Transfer the Fish

Now you can use a small net to lift the fish from the bag and transfer it into the aquarium. For this, brine shrimp nets tend to work very well since they are small and gentle. They can also fit inside small bags.

If you only have a large fishnet, consider using the bucket method – hold the net over a bucket and carefully pour the fish and its water into the net. Then, you can quickly make the transfer into the tank.

Clean Up

Dump the water from the fish bag into the sink or toilet. Do not dump it into the aquarium. To replace lost water from the transfer process, use tap water that has been dechlorinated.

Pearl gourami and rosy barbs in plastic bags


  • Leave the light off for a few hours to allow your fish to adjust without being stressed out by the light.
  • If you’re worried that your fish may pick on the new guy, add a pinch of fish food into the aquarium when you make the transfer. This should take their attention away from the new addition.
  • To ensure that you give your fish enough time between water additions, consider setting a timer on your phone or oven.
  • Make sure you have all your equipment before attempting to add a new fish. This includes a net, dechlorinating solution, and a bucket just in case. Most of the time, these items can be purchased in an aquarium kit at your local pet supply store.
  • If your new fish wants to hide right away, let it. The poor creature is likely scared so if it wants to hide in an aquarium cave for a few hours, there’s no reason that it shouldn’t be allowed to.

Quarantine Tanks for New Fish

Ideally, all new fish should be placed in a quarantine tank for two weeks before they are moved into their new tank. Quarantine tanks are exactly what they sound like – tanks where fish can be quarantined from others.

The purpose of this is to give you time to observe your new fish and take note of disease or any other issues without risking any harm coming to your other fish.

If you notice a disease or fungus, you’ll be able to treat the fish with either chemical medications or a UV sterilizer that is specifically designed for aquarium use.

If you have an extra tank available for quarantine, please feel free to use it! When you do, though, be sure to acclimate your fish the way you would if you were adding them to their permanent tank.

If you don’t have a quarantine tank, just make sure that you buy your fish from a reputable seller and avoid buying any fish that look unwell.


Now that you know how to add fish to a tank, you can feel confident about growing the size of your fish community. You no longer have to wonder how to add new fish to aquariums. Isn’t it great?

Just be sure to take the time to complete the acclimation process properly and, if you can manage it, quarantine your new fish first.