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Acclimating fish from pet stores is a critical part of the hobby to understand. There have been many times when I've seen new aquarium hobbyists acclimate their fish on Tiktok, and the comment section is a forest fire of arguments. "That's not how you're supposed to do it!", "You're killing your fish!", "You're going to shock them with different water parameters.", "Don't add the LFS water into your tank!".

  Float the sealed bag in your aquarium for at least 15 minutes but no longer than one hour to allow for temperature acclimation. The water in the bag should be the same temperature as that of your tank prior to proceeding to the next step.

Let's Dive Into Why.


First of all, there are three ways you can acclimate new fish... each with its own flavor of how. 

1) Bringing home fish from you LFS (local fish store) that are considered hardy

2) Bringing home more sensitive fish from your LFS

3) Receiving fish through the mail

All new fish being put into a community tank should be quarantined for two weeks, at least, before adding them into your aquarium.

Each method has the same 1st steps.

a) Inspect the fish for any deaths

b) Turn off the aquarium lights

c) Float the bag in the aquarium for 20-30 minutes so the water temperature inside the bag equals the temperature outside of the bag.

Once you have floated the fish for 20-30 minutes the steps for acclimation can take vastly different directions. If the aquarium water from your LFS is the same as your home aquarium, then you can simply grab your water change bucket and net, and dump the fish and water into the net with the bucket underneath, and then add your fish directly into the tank. We don't add the LFS water into the tank because we want to reduce the chances of spreading diseases from the store into your aquarium. If the water chemistry is different (for example if your LFS is located in a different city/state/water source), or you have purchased sensitive live-stock like shrimp, then I'd recommend the following.

1) For Hardy Fish: After steps a-c above, open the bag and pour some of your tank water into the bag every 10 minutes until the water volume has doubled... then follow the above bucket and net method of adding the fish to the tank.

2) For Sensitive fish: Drip Acclimation. This method can take 1-2hrs and it requires using some air line tubing as a siphon, tying a knot in the end so you drip water into the fish bag at a rate of 1 drop a second. Afterwards... following the above bucket and net method of adding your fish to the tank.

Some say that fish can last 9 or 10 hours in a bag (or even a day or two in some cases). However, it's best for you and your fish if you stick to leaving your fish in the bag for 5 to 7 hours. A lot of fish can stay alive without oxygen for 2 days in shallow water.

When you buy fish online, there's a lot going on inside that bag. Let's break it down;

Fish traveling inside a bag through the mail are breathing. Exchanging Oxygen for CO2. This carbon dioxide will lower the pH of the bag over time (making it more acidic). This changes the water chemistry inside of the bag, and one of the outcomes is that toxic ammonia is converted into more non-toxic ammonium. Fast forward to when you receive the fish, float the bag for 20 minutes... and if you were to drip acclimate or add in cups of water, all that CO2 in the bag escapes, the pH swings the other way as it gets less acidic, and the non toxic ammonium turns into ammonia. This can shock your fish.

When you get fish in the mail follow these steps;

a) Inspect the fish for any deaths

b) Turn off the aquarium lights

c) Float the bag in the aquarium for 20-30 minutes so the water inside the bag equals the temperature outside of the bag.

d) Grab your net and bucket, dump the fish in the bag into the net with the bucket below, and then add your fish into the new tank.


The answer to this is that fish are really sensitive to big changes in temperature, and ammonia burns can cause or provoke disease. Changes in water chemistry like pH, kH, TDS, etc. adjust within the fish on a daily/weekly time scale... unlike temperature which happens in minutes.

When you bring new fish home they will need to be acclimated to their new environment, mainly the temperature of the water.

As always, comment below with your experiences! Tell me what you do.

Happy swimming!



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