How To Acclimate Your New Fish: Best Tips & Methods

Alison Page

Alison Page


Acclimation Fish

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When you bring any new fish or livestock home from the fish store, you shouldn’t simply drop them out of their plastic bag straight into your fish tank! Instead, your fish must go through the correct acclimation process.

Correct acclimation helps your new fish to adjust to the unfamiliar parameters of the tank water in your aquarium. This prevents the fish from becoming stressed and succumbing to sickness and diseases.

So, we’ve put together this guide to show you how to acclimate your new fish correctly. Note that the procedure is the same for tropical, coldwater, freshwater, and saltwater fish.

Keep reading to find out more…

Why Acclimate Your Fish?

Fish and other aquatic creatures are highly sensitive to fluctuations and changes in their environment. If the water conditions are unstable or unsuitable for the fish, they will quickly become stressed. Stress causes the fish’s immune system to be compromised, leading to disease and sometimes even death.

When you buy your fish, they will be packaged in pet store water that will most likely have a different water parameter from that in your home fish tank. For that reason, it’s essential to acclimate the fish properly when introducing them to your aquarium.

Acclimation ensures that the fish and other livestock can adjust to the different water chemistry in your tank, ensuring that they remain healthy.

The acclimation process must start as soon as you bring your new fish home!

How to Acclimate Your Fish

Once you’ve prepared your aquarium for acclimating your fish, you can head down to the fish store and buy your new pets. As soon as you get home with your fish, the acclimation process can begin.

There are two common fish acclimation methods; the float or bucket acclimation method and the drip acclimation method, and we’ll cover both of them in this guide.

However, whichever method you choose, you should follow these two preparatory steps:

Create a Stress-Free Environment

Start by creating a stress-free environment for your fish.

Turn off all your aquarium lights to help reduce stress on your new livestock. Don’t worry about your plants; although live plants need light to grow and thrive, depriving them of light for an hour or two won’t harm them.

Bright lights can be extremely stressful to fish. By keeping the tank in darkness, you’re giving them a chance to orient themselves in their new environment, which is especially important for shy freshwater species.

Clean Up

Substances such as hand lotions, perfumes, cleaning products, etc. are potentially very harmful to fish.

So, before you do anything else, thoroughly wash your hands to prevent toxins from getting into the aquarium water!

Float Acclimation Method

First of all, let’s look at the float acclimation method.

Acclimation Temperature

Many fish species are extremely sensitive to variations in water temperature. So, one of the most important factors in acclimating fish is ensuring that the temperature in their transport bag is the same as that in the tank.

If you were to simply put the fish straight into the tank from the plastic bag, there’s a danger that the creatures could suffer from temperature shock, which could potentially be fatal!

So, to avoid thermal variation, float the sealed plastic bag in your fish tank for a minimum of 15 minutes to allow the water temperatures to equalize. Do not leave the bag floating for more than one hour.

If you leave the fish in the sealed bag for too long, the oxygen content in the water will fall to dangerous levels.

Also, there’s a risk that harmful waste substances could rise to toxic levels, presenting an additional risk to your new fish.

Water Acclimation

Once the bag has been floating in the aquarium for 15 minutes, carefully use the scissors to cut the bag open, as close to the top as possible. 

Fold the top edge of the bag over to around 1 inch or so. This creates an air pocket within the lip of the bag and keeps it floating on top of the water.

Alternatively, if you’re concerned that the bag might sink, fix it to the side of the aquarium with an algae clip.

Add Aquarium Water to the Bag

Now, take a cup of water from the aquarium and slowly add ¼ to ½ of the cup to the plastic bag. We recommend that you use ¼ cup for smaller plastic bags and ½ cup for larger ones.

Continue adding water every five minutes or so until the plastic bag is full.

Discard Some of the Water

Now that the bag is full, remove it from the fish tank and discard around half of the water into your bucket.

Take great care that you don’t frighten your fish!

Re-float the Bag

Place the bag into your tank and carefully add up to ½ cup of water from the aquarium every couple of minutes until the bag is full.

This helps to further acclimate the new fish and gets rid of most of the original water that was still in the bag.

Carefully Empty the Bag

When the bag is full, take it out of the fish tank and gradually pour off as much of the water as you can into the bucket.

Be very careful that you don’t frighten or harm your new fish during the process.

Add Your Fish to the Aquarium

Now comes the exciting part!

Carefully take hold of the bag by its bottom corner and slowly lower it into the aquarium. Tip the bag so that your fish can swim out of it into the tank.

If you have an invertebrate, you’ll need to immerse the bag entirely and very carefully remove the invert. If you have corals, only handle them by the base.

Any water that’s left should be emptied into a bucket or down the sink, not into the fish tank.

Drip Acclimation Method

Acclimation Fish

Now, let’s find out more about using the drip acclimation method. The main downside to this effective acclimation technique is that it is quite slow. However, some species can need a long acclimation time, and this method tends to be most suitable for those types.

You can create a drip acclimation kit from a length of airline and an air valve. If you prefer, you can buy a ready-made drip acclimation kit.

Put the Bag into a Bucket

Start by placing your fish into a container or bucket that’s large enough for the fish to be covered with enough water that they can swim around. 

Put the bucket on the floor next to the aquarium.

Test the Water

The next step is to test the water pH, temperature, ammonia level, and salinity in both the aquarium and the bucket.

If the variance between the two is considerable, a longer drip acclimation time will be required.

Set up the Drip Acclimation

Take some plastic tubing and an air valve. Set up a siphon drip line into the bucket from the fish tank.

Start the siphon, slowly allowing the water from the fish tank to drip into the bucket. You can use the air valve to adjust the drip rate to between two and four drops per second. That rate will add between 1 and 3 cups of water per hour.

Re-test the Water

Once the water in the bucket equals around twice the original water volume of the bag, you need to test the water again to see if the parameters match those of your aquarium water. If not, continue the drip acclimation.

When the water parameters match, acclimation is complete.

Add Your New Fish to Your Aquarium

Now, you can carefully remove the fish from the bucket and add them to your aquarium.

Do not put any of the bucket water into the fish tank. Instead, use new water to top up the dripped water, as you would when carrying out a partial water change.

Drip Acclimation Method Downsides

There are a few downsides to using the drip acclimation method:

  • This method is pretty slow, often taking up to two hours to complete, depending on the size of the bucket you use.
  • Setting up a drip line is more fiddly and time-consuming than other common fish acclimation methods.
  • If you need to acclimate more than one fish, you’ll need to use a large bucket to avoid potential fighting and injuries.

Top Acclimation Tips

Here are a few very important tips to ensure that the acclimation process goes smoothly.

Don’t Rush It!

Although you’re sure to be in a hurry to get your beautiful new fish into the aquarium, you must not rush the acclimation process.

Generally, wild-caught fish are used to seasonal variations in temperatures and water conditions, but the acclimation should ideally be a slow process.

Don’t Panic!

Even if your fish or inverts look lifeless, you must stick religiously to the acclimation procedure. Some fish species, especially freshwater fish and invertebrates, can look dead, but many revive once the acclimation process is complete. So, be prepared to allow plenty of acclimation time before you give up hope. 

Saltwater fish tend to be somewhat more resilient to relocation, even those that are wild-caught. That’s most likely because these fish are used to the seasonal variation of conditions in the ocean, which is less common in freshwater environments.

Coral Acclimation

Some species of coral can produce a lot of slime under the stress of transportation, and a careful acclimatization process can help to overcome that.

Once the acclimation period has ended, without removing the coral from its bag, hold the coral by its skeletal or rock base and very gently shake it. Avoid touching the fleshy part of the living coral.

Many coral species will not open for a few days following the introduction to their new saltwater aquarium home. That’s quite normal, and the corals should open and begin feeding as normal within a few days.

Don’t Use a Net

Although it might seem like a good idea, never pour your new fish into a net.

This can cause problems by removing the fish’s protective slime coating, leaving them vulnerable to disease. 

Instead, always release the fish directly from their bag.

Don’t Use an Airstone in the Bag

Never place an airstone in the bag during the acclimation process. Airstones can increase the water pH in the bag too rapidly, exposing your new fish to dangerous levels of ammonia. 

Keep the Lights Off

You can help to achieve a positive acclimation response and keep stress levels to a minimum by keeping your aquarium lights turned off for a few hours once you’ve introduced your new fish and other livestock to your freshwater aquarium. 

Stable Water Parameters

All aquatic life needs correct and stable water quality to remain healthy and thriving. That’s especially true of saltwater tanks, where the correct salinity parameters are crucial.

If you have invertebrates, you must acclimate them to a specific gravity of 1.023 to 1.025 to avoid causing the creatures severe trauma or stress.

Use an aquarium water testing kit each day for the first week or so following the introduction of your new livestock. Any fluctuations in water conditions or signs of increasing toxicity must be dealt with and corrected immediately. 

Tank Mates

Sometimes, new fish can be harassed or chased by some of your existing fish, especially if you keep aggressive species. This stress can cause disease outbreaks and even result in mass fish kills. So, how can you prevent that?

  • Feed your existing livestock before you introduce anything new to your tank. This will help to prevent aggression.
  • You can help prevent territorial aggression by moving the décor in the aquarium or changing the layout completely. That way, any territorial fish will need to establish new territories rather than feeling that they have to defend existing ones from the new arrivals.
  • If your tank contains aggressive fish, scoop them up in a plastic critter keeper to keep new arrivals separate from your existing livestock for a few hours. Your new fish can explore the aquarium without being hassled by an existing, belligerent tank mate, which reduces stress on your new fish and can help to prevent any fights and injuries.

Final Thoughts

To give your fish the very best start in their new home, you must take the time to acclimate them properly first.

If you don’t acclimate your fish properly, they will become stressed and vulnerable to disease. So, don’t try to cut corners in your haste to add your new fish to your aquarium!

There are two common fish acclimation methods that you can choose from; the float and drip methods. Both are highly effective, although the drip method is slower and more suited to species, such as marine shrimp, that often take longer to acclimate than other creatures.

Which acclimation method did you use? Tell us in the comments box below.

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