How to Acclimate New Fish

Bringing home a new fish is exciting. But it is also a time when fish are most vulnerable. Many new aquarium owners are disappointed when a fish dies within a few days of adding it to the tank. It is easy to think that the fish was unhealthy, but the real problem here is improper acclimation. 

Fish need some time to adjust to changes in the water temperature, pH, and other water conditions. If you are moving them to a new aquarium too quickly, the sudden changes can cause stress, making them more likely to become sick or die. A common mistake is to float the unopened bag in the aquarium for a few minutes to match the temperature, then pour the fish and the bag's water into the tank. Floating the bag can help equalize temperatures, but you should never add pet store water to your aquarium. Store water can contain bacteria, parasites, and other harmful organisms that can spread disease to your existing fish. 

Instead, use a slow and careful acclimation process. It gives your fish enough time to adjust to their new environment, reducing stress and helping them settle into their new home safely. Remember that proper acclimation can lower stress, but it can't prevent diseases or parasites that a new fish is already carrying. For the best protection, you can quarantine a new fish before adding it to your main aquarium.

Check out Why Calm Water is Crucial for Reducing Fish Stress and Promoting Growth.

How To Add Fish To An Aquarium?

Open the Fish Bag and Let It Float

When you bring your new fish home, dim or turn off the aquarium lights. It helps reduce stress and gives the fish a calmer environment to adjust. You need to be careful when opening the fish bag or removing the rubber band or tie. 

Put that open bag in your aquarium so it floats on the surface. To keep it upright, roll the top edge of the bag down a few times. It traps air inside the rolled edge and helps the bag float without tipping over. If the bag does not stay upright, roll the top down a little more till it floats securely. It becomes easier to begin the acclimation process without spilling the water.

Slowly Add Aquarium Water To the Bag

When the bag floats securely, start mixing your aquarium water slowly with the water in the bag. Add about 1/2 cup (120 mL) of aquarium water to the bag. Then wait for about 15 minutes and repeat the process a few times. 

When you add the water gradually, your new fish gets enough time to adjust to differences in pH, temperature, hardness, and other water conditions. The slow acclimation can reduce stress and lower the risk of shock. 

Check Water Quality

Before you add new fish to the aquarium, make sure the water is healthy and suitable for them. Test the water regularly and make sure important parameters are within the recommended range. 

Those include nitrite, nitrate, ammonia, pH, carbonate hardness (KH), water hardness (GH), and temperature. Only introduce new fish when your aquarium is fully cycled and the water quality is stable. When the water conditions are healthy, your fish gets the best chance of settling in successfully.

Compare the pH of Both Waters.

When your fish is acclimating, check the pH of the water in the transport bag, then compare it to the pH of your aquarium. If the aquarium is close to your home, the pH in the bag is usually close to the aquarium's pH. However, if you have been keeping fish in a bag for many hours, the water chemistry changes. Over time, the fish release carbon dioxide and waste into the bag, which can lower the pH and increase ammonia levels. 

Handle pH Differences Carefully.

If the pH difference between the bag water and your aquarium is less than 0.4 pH units, you can add the fish after completing the water-mixing process and matching the temperatures. If the difference is more than 0.4 pH units, continue adding small amounts of aquarium water to the bag over a longer period until the pH approaches the tank's water pH. 

It gives the fish more time to adjust and reduces the risk of pH shock. Some fish, such as discus, are very sensitive to changes in pH and need a longer acclimation period than harder species. 

Aquarium pH Crashes: What Causes Them and How to Fix Them Fast

Transfer The Fish To The Aquarium

When the temperature and pH of the bag are close to those of your aquariums, you need to move the fish into its new home. Use a soft aquarium net to gently lift the fish out of the bag and place it in the aquarium. You need to be careful not to damage the fish's fins when transferring it. 

Important: Avoid pouring the water from the transport bag into the aquarium. Pet store water can contain bacteria, parasites, or other harmful organisms that can affect your tank. Simply discard the bag of water after you remove the fish. 

Watch The Fish Closely

After you introduce the new fish, keep an eye on it for the next few hours and over the following few days. Make sure the other fish are not nipping, chasing, or bullying the newcomer. 

A useful trick is to feed your existing fish shortly after adding the new one. It keeps them occupied and can reduce aggressive behavior when the new fish settles in. If possible, quarantine new fish for 2-4 weeks before adding them to the main aquarium. It helps prevent disease from spreading and gives you time to ensure the new fish is healthy before you introduce it to the tank.

Prevent Problems During Fish Acclimation

The biggest risks when adding new fish to the aquarium are pH shock. It happens when the pH of the bag water is different from that of the aquarium. Even a small difference can stress your fish, and a large one can be dangerous. The greater the difference in pH, the harder it becomes for a fish to adjust. That's why it is important to acclimate fish slowly rather than moving them directly into the tank. 

Before you buy a new fish, find out the recommended pH of their species. Most freshwater aquarium fish do well when the pH is between 7.0 and 8.0. However, some species prefer more acidic or more alkaline conditions. Remember that your aquarium's pH can naturally decrease over time when fish produce waste and organic matter breaks down.