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How to acclimate new fish to tank? Methods & tips

22 11, 2023

When introducing new fish to your aquarium, it's critical to acclimate them properly to their new environment. This can be a delicate process, but with the right methods and tips, fish acclimation can be a breeze. This guide will help pave the way for a successful transition and a healthy, comfortable home for your aquatic creatures.

Why should you acclimate your new fish?

Not allowing your fish sufficient time to adjust to your aquarium, or simply emptying the entire bag into the tank, can pose significant health risks to both the new fish and existing species in the tank. The water from the fish store may harbor harmful diseases, and not taking the necessary precautions when changing this water for new fish can expose them to various health hazards.

New fish can experience shock due to the abrupt transition into a new environment. Many fish species are notably sensitive to swift alterations in water conditions, resulting in the new fish undergoing shock from unfamiliar surroundings.

This abrupt adaptation can induce excessive stress in your fish, making them more prone to sickness. If the fish doesn't die from the shock outright, it could become more susceptible to disease and illness.

How long to acclimate new aquarium fish

When introducing new fish into the aquarium, it is essential to give them time to acclimate to their new home. This process involves gradually adjusting the temperature of the fish bag to that of the aquarium.

Put the fish bags in the aquarium or sump. It can take 15 to 30 minutes for the temperature in the aquarium to equilibrate. This process will reduce stress on the animals when they are placed in the tank. However, before you do that, we recommend reducing light intensity into aquarium or totally off.

Keep in mind that fish purchased online stay in total darkness for several hours or more. Sudden exposure to strong light is very detrimental to their organism. This makes the fish more stressed and thus excrete more ammonia, which reduces the fish's chances of survival.

How to properly acclimate fish?

We recommend quarantining every new fish. This process can be carried in other small quarantine tank or big bucket. During quarantine, you need to ensure light, warming, and filtration. The time of quarantine shouldn't be shorter than 2 weeks. Then you should observe the behavior of fish, and whether there are symptoms of disease.

In case that you detect any diseases, you need to start treatment. Diseases in the target aquarium could contribute to the death of the fish and invertebrates kept there.
You can find more information on why quarantine is so important here.

No matter which way of acclimatization and quarantine fish you will choose, you have to prepare yourself a freshly made brine in a volume of 5 to 20 liters. It's crucial because when taking water for acclimatization from the aquarium, make up the shortfall with fresh water.

Let's move on to acclimatization methods for our fish!

Acclimating with the Floating Method

1. Float the bag

  • On the start, place the bag with your fish in their new habitat while it is still closed for at least 20 minutes. If your fish isn't in a bag, you should put them in one and securely seal it. Ensure the water's flow in the tank is not so powerful to toss the fish bag around.
  • Turning off the light in the aquarium during this process is also recommended. As a strong light close to the bag could rapidly warm up the water inside the bag, potentially causing stress to your fish. Taken out of a dark thermobox and exposed to strong light, the fish will start to become more stressed.
  • Monitor your fish attentively to watch for any signs of stress. These could be a sudden change in your fish's color, an absence of interest, or your fish seeming to breathe rapidly.
  • If they show any of these signs, remove the bag from the tank and observe their behavior after approximately 5 minutes. Use your test kit to check the tank water to make sure it is suitable for your fish.

2. Time to add water from the aquarium

  • Once 20 minutes have passed, carefully open top of the bag containing your fish and pour the contents of the bag into another container (plastic container or bucket). We then add water to it with a volume of 50 to 100% of what was in the bag. After two to five minutes, we gently pour half the water out of the bucket and add the same volume of aquarium water.
  • Repeat this process two or three times.
  • We can then let the fish into the aquarium, but we do this without pouring the water from the bucket into the tank.

Acclimating with the Drip Method


We can only acclimatize in this way if we have bought the fish from a local shop and the fish has arrived at our home in less than 3–4 hours. Carrying out this type of acclimatization on fish that have been in transit for several hours or more can contribute to their death within hours of being released into the aquarium. Why does this happen? We already explained:

During transport, fish take up dissolved oxygen in the water and excrete carbon dioxide. This causes an increase in both carbon dioxide and ammonia levels in the bag. When the fish are in a sealed bag, carbon dioxide levels rise, which simultaneously lowers the pH. The lower pH ensures that the ammonia remains in a non-toxic form. Opening the bag triggers a series of individual reactions one after the other, a chain reaction, and the parameters quickly begin to change. The bag is opened, carbon dioxide is released and oxygen begins to flow in. Oxygen raises the pH level. The sharp rise in pH causes the ammonia, which is in a non-toxic form, to convert to a toxic form and can damage the gill tissue of the fish, leading to poor welfare and possibly causing the animals to die.

However, death does not necessarily occur immediately. It can occur after a day or two or later. The rate of increase in ammonia toxicity depends on several factors, including the amount of ammonia in the bag, the rate of oxygen transfer into the water and the rate of increase in pH. Therefore, under no circumstances, air pump aeration of the water should be used during acclimatization.

1. Introduction

This solution is an excellent choice for more sensitive fish and invertebrates, as shrimp or sea stars. To implement the drip technique, you will need a few components.
The following are required for this drip operation:
Aquarium-designated buckets with a capacity of 12 or 20 liters.
Additionally, airline pipes will also be required.

2. Introducing the Fish

Pour the contents of the bag provided by the fish store into a bucket that you intend to keep near the fish tank where the new fish will be transferred. Make sure to pour adequate water to completely cover the fish.

3. Setting up the Siphon

Configure your siphon, hose, and hose valve to slowly and gradually acclimate aquarium fish. Utilize the air valve, clip, band, or loose knots to effectively control the flow and begin acclimating your fish. The flow rate should be about 2–3 drops per second.

4. Pour out 50% of the water

When you notice that the second amount of water has arrived, as at the very beginning, pour 50% of the water out of the bucket. Put the tube in the bucket again and wait until the second amount of water has arrived once more. The whole process can take between 30 minutes and an hour. If the acclimatization process is long in this way, a heating system should be provided for the fish so that the water temperature does not fall below that of the target aquarium.

5. Move your fish to the primary aquarium

Once acclimatized, we introduce the fish into the aquarium, and we do this without pouring water from the bucket into the main aquarium.
Both methods can be used on freshwater fish and saltwater fish.