Methods to Introduce New Fish To An Established Tank

When you buy a fish from the pet store, the fish are usually placed in a plastic bag. Many beginner fish owners make the mistake of adding their new fish from the bag into their established tank without doing anything to prepare them first. We don’t recommend adding them without a few steps between because it can be harmful to both your new fish and your existing fish in the established tank. 

An acclimation period is helpful for both new and longtime residents of your aquarium. During the acclimation period it eases the new fish into the tank water you have, making the transition easier for them. Not doing this is the reason why some new fish die not long after being introduced to an established tank.

The reason why they might die is because the water in the plastic bag has water that may have different water conditions than your aquarium. Introducing new fish to your established aquarium can stress your fish because of a sudden change in the environment. 

The water in the bag can also carry diseases and bacteria that can be harmful to the fish in your aquarium. Adding that water could unintentionally introduce disease or illnesses into your aquarium.

There are a few methods to greatly reduce their stress. The new fish first needs to be acclimated to the water conditions in your existing aquarium. Acclimation is the process of adding fish to an established tank while minimizing the stress to them. This involves gradually getting them used to the water conditions of your established tank.

There are 3 methods to acclimate new fish to an established tank:

  1. Drip Method
  2. Acclimating in a Plastic Bag
  3. Quarantining New Fish

Method 1: Drip Method

Things needed:

  • Gravel vacuum
  • 5-gallon plastic container or pitcher
  • Aquarium testing kit

Because you are introducing your new fish to an established tank, you should already have this equipment. This method should be used if you do not have a quarantine tank. It is not difficult to do and is the fastest way.

Transfer the Fish to a Container

Take the plastic container or pitcher and place your new fish along with the water in the bag into the container. Make sure to use a plastic container that isn’t wide. If it’s wide it means there will be less depth in the water and make it hard for your fish to swim. 
If you do not have a narrow container, you can increase the depth by tilting the container slightly to the side. Later when more water has been added to the container, you may not need to tilt the container.

Siphon Water from the Established Tank

After transferring the fish to the plastic container, take out your gravel vacuum. The gravel vacuum needs to be used to siphon water from your established tank to the holding container. To start the siphon you can follow the same process that you use to perform water changes. You only want to get regular aquarium water, make sure not to suck the gravel, or any of the waste in the gravel. Another way to get the water is to use a water pitcher and pour it into something that can drip water.

If your vacuum has a siphon valve, you can use that to control the flow of water. The flow should be 4-5 drips per second. If your vacuum does not have a siphon control, you can put clips on the tube to regulate the flow. Move the clips to increase or decrease the water flow as needed.

Let the water drip out and wait till the water has doubled in the container. This will likely take a few minutes.

Remove Half of the Water

Once the water volume has doubled, remove half the water from the container. Start the siphon to again double the water. After the water has doubled in the container the new fish should have acclimated to the water conditions of your established tank. This entire process could take up to 30 minutes. If you wanted you could do this again one more time just give a little more acclimation time.

Check the water conditions in the holding container and your aquarium to make sure they are the same. If they are, you can move your new fish to your aquarium. 

Add Your Fish to Their New Tank

The fish are now ready to be added to your tank but there are a few things that need to be done. If there are other fish species in your tank, feed them before adding the new fish. This will reduce the aggressiveness your existing fish may have towards your new fish. 

The lights inside the tank should be turned off. Turning the lights off inside the tank will make it difficult for other fish to spot the new fish. It will also help reduce the stress the new fish may feel. 

If you want to rearrange or add new decorations inside the tank do this before adding new fish. Once your aquarium set up is ready, use a clean net to catch the fish from the container and move them to your aquarium. Repeat the process to add more fish from the container. 

Don’t add the water that is inside the container to your tank. It has water from the fish store that can be harmful to your existing fish. The water from the fish store may contain pathogens or diseases from the pet store aquariums.

Keep the lights turned off for 3 to 4 hours and dim the room lights if possible. By keeping the lighting lowered you give the new fish time to settle in without it being obvious to your existing fish. After a few hours they should have found a few places to hide from any possible aggressive fish.

Method 2: Acclimating the Fish in the Plastic Bag

For some the Drip Method may seem complex and they may prefer to acclimate their new fish in the plastic bag itself. While this is as effective as the drip method, acclimating the fish in a plastic bag can take a lot more effort and time.

Float the Plastic Bag

The first step is to make the water temperature inside the plastic bag is the same temperature as the inside of your tank. To get the temperature the same take the sealed plastic bag that has the new fish and float it in your aquarium. 

After 15 minutes open the seal of the bag and make a few folds on the top edge of the bag. This will help to create air pockets that should allow the bag to float. While doing this be careful not to spill any water from the bag into your aquarium. If making folds to keep the bag floating doesn’t sound appealing you can get clips for the bag. The clips will let you attach the bag to two walls of your aquarium, making it more secure so water won’t spill out.

Test Water Conditions

Test the water conditions like pH and temperature inside the plastic bag and your aquarium. The temperature should be the same now. Compare the pH levels and note the difference. A difference of 0.2 is acceptable but if it is more then more water needs to be added inside the plastic bag.

Add ¼ cup of aquarium water into the plastic bag every 15 minutes. Keep doing this until the pH of water inside the plastic bag matches the water in your aquarium. If the bag fills up, you can empty ¼ cup of water before you add more.

Add Fish to Your Aquarium

Once the pH is equal you can add your new fish to your tank. Before adding the new fish, turn off the lights inside the tank and feed the existing fish. Feeding the fish in your aquarium will make them less aggressive towards your new fish. Keeping the aquarium lighting lower will make it harder for your existing fish to spot new fish. It also gives your new fish some time to find hiding places. 

Use a fish net to scoop your new fish to add them to your tank. Avoid adding the water from the plastic bag to your fish tank. The plastic bag has water from the fish store that could be harmful to your aquarium. Drain the water from the plastic bag into the sink and discard the bag. 

Adding water to the plastic bag has lowered the water level inside the tank. If it’s not a lot lower you can wait until the next time you do a water change. If you lost a lot of water go ahead and fill your aquarium back up sooner.

Method 3: Quarantining the New Fish

Things needed:

  • A quarantine tank with equipment
  • Aquarium testing kit

Quarantining a fish involves keeping your fish in a small aquarium for a few weeks before introducing them to your community fish tank. We recommend quarantining all new fish for at least 2 weeks. This has several advantages, the main one is preventing the transfer of harmful diseases to your main aquarium. 

The pet store has new fish from all over, and the water may carry diseases and pathogens that can be harmful to your existing fish. Keeping the new fish in a quarantine tank will help you identify if the new fish are healthy or not. If you find any diseased fish, you can prevent the spread of diseases to your main aquarium.

Setting up a Quarantine Tank

The quarantine should be at least 5 to 10 gallons. It should have all the equipment like a sponge filter and aquarium lights. The best set up will be one that is similar to your main aquarium.

The tank should be cleaned thoroughly before adding the new fish, so that any bacteria from old quarantines will not survive to this use. You will also want to make sure that the water has been completely cycled. Cycling makes sure toxins like ammonia do not build up and poison your new fish.

Add Fish to the Quarantine Tank

After setting up your quarantine tank add the new fish inside the tank. We like the floating method discussed earlier for this. Place the plastic bag inside the tank and let it float for around 15 minutes. Floating them will help the water temperature in the plastic bag become the same as in the tank. 

Once the temperature has stabilized, open the bag and add water from the quarantine tank to the plastic bag. The plastic bag should have 50% pet store water and 50% tank water. Don’t add the pet store water inside the bag to your tank because this can contaminate the tank water.

Let the bag float for another 20 minutes. 

After 20 minutes use a net to catch the fish and add them to the tank. Discard any water in the bag down the drain.

Observe the Fish

When your fish have been added to the quarantine tank, they should be observed every day to check if they have any diseases or parasites. Signs of unhealthy fish include tattered fins, loss of appetite, listlessness, loss of balance or clamped fins. 

The fish should be kept in the quarantine tank for 2 to 3 weeks. If your fish are healthy you can add them to the established tank.

Add the Fish to Your Tank

Place your fish in an aquarium bag and acclimate them. Your fish needs to be acclimated using the same process mentioned in the previous method.

Before adding the new fish, feed the existing fish inside your tank. Then turn off the lights.

Use a net to catch the fish from the bag and add them to the tank. 

Discard any water from your quarantine aquarium. Completely wash out the empty tank and boil any rocks you have. A thorough cleaning ensures the next time you want to quarantine fish your quarantine tank will be completely clean and ready for use.