How To Acclimate A Fish & Why You NEED To!

Last Updated on 2023-10-04

Acclimating your fish to its new environment is a critical step in ensuring its health and happiness in your aquarium. Whether you’ve just brought home a new fish from the store or received a shipment, proper acclimation can make all the difference in helping your aquatic pets settle into their new home.

This article covers the essential steps for acclimating fish, for beginners and experienced ones. So, keep reading to find out everything you need to know!

How To Acclimate Your Fish (Store Bought)

When introducing new fish to your tropical aquarium, acclimation is crucial for their health and well-being. Here are the step-by-step instructions for acclimating your fish effectively:

  1. Prepare Your Aquarium: Make sure that the tank you’re about to add your fish to have all the water requirement parameters they need. Generally, for most tropical fish, this means the pH will need to be between 6.0-8.0 the temperature will need to be between 70-80°F, and the ammonia will need to be at 0ppm.
  1. Turn Off Lights: Dim the lights in your aquarium to reduce stress for both your existing fish and the newcomers.
  1. Float the Bag: Gently place the sealed fish bag or container on the water’s surface in your aquarium. This allows the temperature inside the bag to gradually match the tank’s temperature. Leave it for about 15-20 minutes.
  1. Monitor Temperature: After the floating period, check the temperature inside the bag. It should now be close to your aquarium’s temperature.
  1. Open the Bag: Carefully open the bag, rolling down the top edges to create a floating collar. This prevents water from mixing between the bag and the tank.
  1. Drip Acclimation (Recommended): If you have a drip acclimation kit, set it up according to the manufacturer’s instructions. This method involves slowly adding small amounts of aquarium water to the bag over an extended period, typically 1-2 hours. It helps fish adjust to differences in water chemistry.

(If you don’t have a drip acclimation kit however, you can use a small cup to add water from the tank bit by bit)

  1. Net the Fish: Once the fish have been properly acclimated, use a net to transfer them from the bag into your aquarium. Avoid adding water from the bag to your tank.
  1. Observe Your Fish: After introducing the fish, closely monitor their behavior for any signs of stress or aggression. Keep the lights dimmed for the first few hours to help reduce stress.
Prepare Your AquariumEnsure water parameters like pH, temperature, and ammonia are appropriate.N/A
Turn Off LightsDim aquarium lights to reduce stress.1 Day
Float the BagPlace the sealed fish bag on the water’s surface to match temperatures.15-20 minutes
Monitor TemperatureCheck that the bag’s temperature is close to the aquarium’s.N/A
Open the BagRoll down the top edges to create a floating collar.N/A
Drip AcclimationSlowly add aquarium water to the bag over 1-2 hours.1-2 hours
Net the FishTransfer fish from the bag to the aquarium.N/A
Observe Your FishMonitor for signs of stress or aggression.First few hours

How To Acclimate Shipped Fish

Now, here’s a step-by-step guide on how to acclimate your shipped fish, it’s important to remember, that you shouldn’t float a shipped fish as it’s going to impede the gas exchange. If your fish has been shipped from far away, the water will be low on oxygen, so you’ll need to make sure they’re getting enough.

With that in mind, here is what you should do!

  1. Prepare Your Materials: Gather all the necessary materials, including a clean bucket or container, a net, a drip line or airline tubing with a control valve, a thermometer, and a timer or watch.
  1. Turn Off Tank Lights: Before introducing the fish, turn off the lights in the aquarium. This helps reduce stress on the fish during the acclimation process.
  1. Float the Bag: Place the sealed bag containing the shipped fish into the aquarium, allowing it to float on the water’s surface. This will help the temperature inside the bag gradually adjust to the tank’s temperature.
  1. Monitor Temperature: Use the thermometer to monitor the water temperature inside the bag. Ensure that it matches the temperature in your aquarium. This may take approximately 15-30 minutes.
  1. Prepare the Drip Line: While the bag is floating, set up the drip line or airline tubing. If using airline tubing, create a siphon by sucking on one end to start the flow. Control the drip rate with a valve or by pinching the tubing.
  1. Start Dripping: Place one end of the drip line or airline tubing into the bag containing the fish, securing it in place. Adjust the flow rate to create a slow, steady drip. The goal is to slowly add water from the tank into the bag over a period of 45 minutes to 1 hour.
  1. Observe Water Volume: As water drips into the bag, periodically check the water volume. If the bag becomes too full, remove some water to prevent overflow. Continue dripping water into the bag at a steady pace.
  1. Test Water Parameters: After about an hour, test the water in the bag for parameters such as pH, ammonia, and nitrite levels. This will help ensure that the water quality in the bag is safe for the fish.
  1. Net the Fish: Once the fish have been acclimated to the tank’s water parameters, gently net them out of the bag and transfer them into the aquarium. Avoid adding the water from the bag to your tank, as it may contain contaminants.
  1. Discard Bag Water: Dispose of the water from the bag safely. Do not pour it into your aquarium.
  1. Monitor Fish: Keep an eye on the newly introduced fish for signs of stress or illness in the following days. Ensure they are eating and behaving normally.
  1. Gradual Introduction: If you are adding multiple fish, introduce them one at a time, following the same acclimation process for each fish.
Prepare Your MaterialsGather bucket, net, drip line, thermometer, and timer.N/A
Turn Off LightsDim aquarium lights to reduce stress.N/A
Float the BagPlace the sealed fish bag on the water’s surface to match temperatures.15-30 minutes
Monitor TemperatureCheck that the bag’s temperature is close to the aquarium’s.N/A
Start DrippingUse a drip line to slowly add aquarium water to the bag.45 mins-1 hour
Test Water ParametersCheck pH, ammonia, and nitrite levels in the bag.N/A
Net the FishTransfer fish from the bag to the aquarium.N/A
Discard Bag WaterDispose of the water from the bag safely.N/A

How Long Does It Take To Acclimate Fish?

The duration of the fish acclimation process can vary depending on several factors, including the specific needs of the fish species and the method of acclimation you’re using. Generally though, it should only take around an hour to acclimate your fish.

Floating the Bag: The initial floating of the sealed bag or container in your aquarium usually takes about 15-20 minutes. This allows the temperature inside the bag to gradually match the temperature of your aquarium.

Drip Acclimation: If you choose to use the drip acclimation method, it can take an additional 1-2 hours or more. Drip acclimation involves slowly adding small amounts of your aquarium water to the bag over an extended period to help the fish adjust to differences in water chemistry.

The total acclimation time can, therefore, range from approximately 15 minutes to a few hours, depending on whether you opt for the standard floating method or the slower, more precise drip acclimation method.

It’s essential to be patient and allow the fish adequate time to adapt to their new environment to minimize stress and ensure their well-being.

How Long Should Fish Stay In The Bag Before Putting Them In The Tank?

Your fish should usually stay in the sealed bag or container for approximately 15-20 minutes before being introduced to your aquarium. During this time, the bag floats on the surface of the aquarium water. This allows the temperature inside the bag to gradually adjust to match the temperature of your aquarium.

This step is crucial because sudden temperature changes can stress and harm the fish. By floating the bag, you give the fish an opportunity to acclimate to the water temperature in a controlled and gradual manner.

Once the temperature inside the bag closely matches that of your aquarium, you can proceed with the next steps of the acclimation process, such as opening the bag, drip acclimation (if preferred), and transferring the fish into your tank.

Why Is Acclimating Your Fish So Important?

Failing to acclimate fish before introducing them to a new aquarium can have several negative consequences for the health and well-being of the fish:

Temperature Shock

Fish are highly sensitive to temperature changes. Not acclimating them can lead to temperature shock, which can stress and harm the fish. In severe cases, it can even be fatal.


Sudden changes in water conditions, such as pH levels, can cause extreme stress for fish. Stress can weaken their immune systems, making them more susceptible to diseases and illnesses.

Behavioral Issues

Fish that are not properly acclimated may exhibit abnormal behavior, including hiding, erratic swimming, or aggression towards other fish in the tank.

Increased Mortality

Unacclimated fish are more likely to experience health issues and a higher mortality rate. This can lead to the loss of your valuable and often expensive fish.

Water Quality Problems

If water from the fish store or shipping bag is introduced directly into the aquarium, it can introduce unwanted contaminants, parasites, or diseases into your tank, affecting the overall water quality and the health of your existing fish.

How Can You Tell If A Fish Is In Shock?

Identifying whether a fish is in shock can be challenging since fish don’t display shock in the same way humans or some other animals do. However, there are several signs and behaviors that may indicate a fish is experiencing stress or shock:

Erratic Swimming: Fish in shock may swim erratically or appear disoriented. They might dart around the tank or display unusual swimming patterns.

Hiding: Stressed fish often seek shelter and hide in aquarium decorations, plants, or other hiding spots. If a fish that is usually active suddenly hides for an extended period, it may be a sign of stress.

Loss of Color: Some fish may lose their vibrant colors when stressed. They might become pale or develop dark patches or spots on their bodies.

Reduced Appetite: A fish in shock may lose its appetite and refuse to eat. This can lead to weight loss and further weaken the fish.

Gasping at the Surface: If a fish is struggling to breathe and frequently comes to the water’s surface to gulp for air, it could indicate stress or poor water quality.

Lethargy: Stressed fish may become lethargic, showing little to no interest in their surroundings or tankmates. They might hover near the bottom of the tank or in one spot.

Abnormal Fins: The fins of a stressed fish may appear clamped or held close to the body, rather than being spread out as they would in a relaxed state.

Increased Aggression: Some fish may become more aggressive when stressed, potentially leading to conflicts with other tankmates.

Rapid Gill Movement: If you observe a fish’s gills moving rapidly or appearing swollen, it can be a sign of stress, often due to poor water quality or sudden changes in environmental conditions.

It’s important to note that these signs can also be indicative of other health issues or water quality problems. If you suspect a fish is in shock or experiencing stress, it’s essential to address the underlying causes promptly. 

This may involve improving water quality, adjusting tank conditions, or providing a more suitable environment for the fish. If the symptoms persist or worsen, seeking advice from a knowledgeable aquarium expert or veterinarian is advisable to ensure the fish’s well-being.


Acclimating your fish isn’t just necessary; it’s an act of care and responsibility for your fish! And of course, it’s crucial for their health and happiness. Be patient, pay attention to detail and be sensitive to their needs. And because each fish is unique, always adjust accordingly. Enjoy the rewarding journey of being a responsible fishkeeper.

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