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How to safely acclimate your new aquarium fish

If you do not properly acclimate your fish before putting them into your tank, you could end up making them sick and send them to their eventual death.

This guide at Aquarium Blueprints is going to teach you the benefits of acclimation as well as the various methods.

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Why you should acclimate your pet fish

Immediately putting your newly bought fish into your aquarium is an extremely bad idea. This is because your water parameters (such as temperature and pH) will most likely be different than the waters where you got your new fish from.

Throwing your new pet fish instantly into your tank could stress them out and send them into shock, both of these could lead to a weakened immune system, making them more prone to diseases.

Thus, it is best to acclimate your new aquarium fish properly before adding them into your tank.

How to acclimate aquarium fish to temperature

In terms of acclimation, temperature is the most important factor that your fish must adjust to in the beginning. Fortunately, temperature acclimation is easy and mostly hands-free.

To do so, you simply put the bag holding your fish in your aquarium. Do not open your bag just yet. The bag will float and the temperature of the water in the bag will eventually reach an equilibrium with the water in your fish tank. This process will take around 15 minutes although you may want to wait longer if there is a dramatic difference between the two temperatures.

You might want to consider reducing the water flow of your filter while floating your fish bag just so you won’t get any water splashes that end up outside your tank. Alternatively, you can float your bag away from the outflow.

General Tips For Acclimating Aquarium Fish

Avoiding cross contamination when acclimating

Before we begin acclimating the fish to the water parameters of your tank, it is extremely important that you avoid mixing the water from the bag to the water from your aquarium. This is because you don’t exactly know where the water housing your new fish came from. In a worst case scenario, the water in the bag may contain contagious diseases that could spread in your aquarium.

To avoid cross contamination, avoid putting any water from the bag into the aquarium. Therefore, you should use a net to transport the fish to your tank.

How to transport the fish from the bag to the fish tank

If you have a hard time catching the fish, we recommend using a bucket. Place your fish net over the bucket and hold the net firmly in place.

Afterwards, slowly pour out the water from the bag over the netting and into the bucket.

You should be able to catch all the fish this way while limiting the amount of water from the bag from getting into your fish tank.

Once you have all the fish in the net, place your free hand over the top to prevent the fish from jumping put.

After transporting your fish, you might want to consider sanitizing your fishing net and then let it completely dry out.

You should then be able to use your fish net again without having to worry about cross contamination.

To find out how to sanitize your netting, you can check out this guide.

Turn off lighting while acclimating

You should also turn off any lighting you have on and around your fish tank. This is because your fish is already stressed from transportation. Seeing bright lights will only stress them out even more. So make sure to keep your aquarium as dark as possible.

You should probably keep the lights off your tank for at least 24 hours after adding your new fish just so the new inhabitants will feel more comfortable with their surroundings. Not to mention that the other fish most likely bother the new fish in the dark.

Feeding the existing fish in your tank

Before adding your new fish to an already established tank, we recommend feeding the existing fish you already have in your aquarium. There is a possibility, especially if your existing fish is much bigger than the newcomers, that you new fish may be thought as food.

If your old fish have already enjoyed a full meal beforehand, then it is unlikely that they will go after your new fish.

As an extra precaution, try adding your new fish near the bottom of your tank. If you release them at the top, the existing fish may think of them as food since flakes, pellets, and other foods are dropped from the top.

Acclimating your pet fish to water parameters

After acclimating your fish to the temperature, you then have to acclimate them to the water parameters of your fish tank. There are three main methods to do so, all of which will work for most fish and other aquatic species.

How to perform plop-and-drop acclimation

The plop-and-drop acclimation is when, after acclimating your fish to temperature, you immediately net them out of the bag and put them into your fish tank.

This method works because the water in the fish tag is filled with ammonia, especially if your fish has been sitting in it for several days if you ordered them online. In addition to ammonia, your fish will also produce carbon dioxide, which will lower the pH and make the water more acidic. Because of this, the ammonia will be converted to ammonium, a less toxic compound.

Once you open the fish bag, however, you will expose the water to the oxygen in the air. This will cause the pH to quickly rise, which, in turn, will convert ammonium to ammonia.

The plop-and-drop method ensures that you will quickly be able to get your fish from the bag and into your tank after opening the bag, prevent any prolonged exposure to ammonia.

How to perform drip acclimation

Another popular method is drip acclimation. After acclimating the temperature, open the fish bag and pour it into a container capable of holding water. As an extra precaution, we also recommend adding a tiny bit of Seachem Prime (which you can buy on Amazon) to detoxify the potential ammonia that could result from opening the bag. You can then use an airline tubing (you can purchase the Peen Plax tubing on Amazon if you don’t have one on hand) to siphon the water from your aquarium into the container holding your new fish.

To start a siphon, place one end of the airline tubing into your tank. Using your mouth, suck the air out from the other end until you start seeing a rush of water. You then have to loop and/or tie the tubing to restrict the water enough so that you get between 2 to 4 drops of water per second from the tank to the container.

For drip acclimation, the goal is to get around 75% of water from your aquarium and 25% of the water from the bag in the container. If you want to be more cautions, you can aim for a bigger ratio of tank water to bag water. If your container is not big enough, you can remove 50% of the water if it gets close to the top.

Once you feel that enough of your tank water has been added to the container, you can net out the fish from the container and place them in your aquarium.

We feel that drip acclimation is best used for sensitive aquatic life such as shrimp. With that said, this method also works on all types of fish. If there is a big difference in pH in the bag and your aquarium, then we also prefer using drip acclimation over the other two methods.

How to perform floating bag acclimation

The floating bag acclimation is when you acclimate your new fish by adding your tank water into the bag containing your new fish. To do so, open your bag after temperature acclimation (you should also add a tiny bit of Seachem Prime as a precaution to detoxify any ammonia present from exposing the bag water to air) and then roll down the edge top of the bag to at least inch to make sure that it will float and won’t capsize. Doing so will prevent water from the bag from spilling over into the tank.

You can then begin adding small amounts of water from your tank into the bag every five minutes. As we mentioned above, the goal is to get around 75% of water from your aquarium and 25% of the water from the bag. If you don’t have enough space from your bag to do so, you can remove 50% of the water from it once the water level gets close to the top. Once you feel like you reach your goal, take the floating bag out of your tank, net the new fish from the bag and place them into the aquarium.

We don’t recommend using the floating bag acclimation method as it requires more work than the other two acclimation techniques we mentioned in this guide. Not to mention that there is a high risk of cross contaminating your tank water with water from the bag.

Instead of acclimating a floating bag inside your aquarium, we highly recommend using some sort of container outside of the tank that can hold water. You can then begin to add small amount of water from the aquarium to the container without having worry about cross contamination.


Before acclimation the water parameters, you need to first acclimate your fish to temperature. During this time. you should also turn off your aquarium light fixture and feed your existing fish to reduce the stress of your new fish.

The plop and drop acclimation is generally considered the fastest way to introducing new fish to your water parameters. If you have more sensitive fish and/or big differences in pH, then drip acclimation may be a better option. We find that the floating bag acclimation is a too risky as it is easy to cross contaminate the waters of your bag and tank.

When transporting your fish from the bag to your tank, use a container and a net. Pour the bag through the net resting on top of the container to quickly catch all the fish in the bag. Afterwards, quickly put one had over the top of the netting and transfer the fish to your new aquarium.

Keep your lights off for at least 24 hours when adding new fish. You might also want to sanitize the aforementioned fish net if you are planning to use it again in the near future.