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How to Acclimate New Fish & Aquatic Life: Thriving Tank Guide
Published on September 1st, 2022
Updated on October 22nd, 2025
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Overview
Aquatic life is sensitive to rapid changes in their environment. The water that your aquatic life is packaged in most likely has different water parameters than that of your home aquarium. For this reason, proper acclimation is vital when introducing new life into your aquarium. Acclimation helps them adjust to the temperature and water chemistry of your tank, thereby helping ensure the health of your new addition. The acclimation process of aquatic life must begin immediately upon arriving home. To learn more, visit the following guides:
- Setting Up a Freshwater Aquarium
- Setting Up a Saltwater Aquarium
- The Nitrogen Cycle
- Aquatic Water Quality
Supplies needed to acclimate your aquatic life
You need very little to complete the acclimation process:
- Scissors
- Bucket
- Algae clip
- Measuring cup
- Watch or timer
- Towel, to wipe up any spills
How to acclimate your aquatic life
Following are the steps to acclimate your new aquatic life:
- Turn off all aquarium lights and reduce ambient lighting to reduce stress on aquatic life
- Thoroughly wash your hands to remove perfumes, lotions, etc.
- Float the sealed bag with your aquatic life inside, in your aquarium for at least 15 minutes (but no longer than 1 hour) to allow for temperature acclimation; the water in the bag should be the same temperature as that of your tank before proceeding to the next step
- If, for whatever reason, the bag has burst or the water is extremely foul, do not temperature acclimate; proceed directly to step 9
- After floating the bag for 15 minutes, carefully cut it open as close to the top as possible and fold the top edge of the bag down one inch to create an air pocket within the lip of the bag. This will allow the bag to float on the surface of the water—or, if possible, secure the bag to the aquarium side with an algae clip
- Slowly add ¼ to ½ cup of aquarium water to the bag. It may be easiest to use ¼ cup for small bags and ½ cup for large bags
- Repeat step 5 every five minutes until the bag is full
- Once the bag is full, remove the bag from the aquarium and discard half of the water in the bag into a bucket, being careful not to harm or expose your aquatic life to air
- Repeat steps 4–6. This will further acclimate the new aquatic life to your system and will eliminate most of the water originally in the bag
- Once the bag is full, remove it from the aquarium and slowly pour off as much water as possible into a bucket without harming or exposing your aquatic life to air (see step 7)
- Grasp the bottom corner of the bag and lower it into the aquarium
- Lift the bottom corner of the bag and allow your fish to swim out of the bag. If you have an invertebrate, submerse the bag and carefully remove the invertebrate (remember to only handle corals by the base)
- Any remaining water in the bag should be poured into a bucket or sink, not the tank
Additional considerations
- Be patient and don't rush the acclimation process
- Follow the acclimation procedure even if your new aquatic life is inactive and appears to be lifeless. Some fish and invertebrates can appear lifeless when you get them home but may revive when the acclimation procedure is followed correctly
- Do not pour fish into a net. This removes the protective slime coating and makes the fish vulnerable to disease. Always release by allowing fish to swim out of the bag
- Never place an air stone into the bag when acclimating your new aquatic life. An air stone will increase the pH of the water in the bag too quickly and expose your new aquatic life to lethal levels of ammonia
- If possible, keep aquarium lights off until several hours after your aquatic life has been fully acclimated and introduced into the aquarium, as this will help keep the stress level down
- Stable water quality, water temperature and specific gravity are critical to the health of aquatic life, especially invertebrates and marine plants. It is essential to acclimate marine invertebrates and corals to a specific gravity of 1.023 to 1.025, or severe stress or trauma may result. If you are unsure of your water quality, Petco Pet Care Centers provide free water testing
- Some live corals produce excess slime when transported. Following the acclimation period, hold the coral by the rock or skeletal base and gently shake the coral in the shipping bag before placing into the aquarium. Never touch the "fleshy" part of a live coral. Many species of coral will not open for several days after introduction into their new home. This is normal; give them a few days to acclimate to their new home
- It is important to prevent aquatic life from coming in direct contact with air. This is especially important with clams, scallops, gorgonians and sponges
- In some instances, a new fish will be chased and harassed by one, or all, of your existing fish:
- Solution 1: Feed your existing aquatic life prior to introducing any new life. This will help alleviate possible aggressive behavior
- Solution 2: Change or move the décor in your aquarium prior to introducing the new aquatic life. This change will alter established territories and may help alleviate aggression
- Solution 3: A clean plastic critter keeper can be used to contain any aggressive fish within the aquarium for several hours until the new arrival adjusts to its surroundings. Scoop the aggressive fish into the perforated plastic critter keeper and float in the aquarium for several hours while the new tank mate adjusts to the aquarium. By placing the aggressive fish in a perforated critter keeper, you'll reduce the stress on the new arrival as they explore and get familiar with the aquarium without being harassed by the existing fish
FAQs
How long does it take to acclimate fish?
It may take between 15 minutes to 1 hour to properly acclimate your aquatic life.
Notes and sources
Ask a Pet Care Center associate about Petco's selection of products available for the care and happiness of your new pet. All products carry a 100% money-back guarantee.
Because all aquatic life are potential carriers of infectious diseases such as atypical mycobacterium and salmonella, always wash your hands before and after handling your aquatic life or habitat contents to help prevent the potential spread of disease.
Pregnant women, children under the age of 5, senior citizens and people with weakened immune systems should contact their physician before purchasing or caring for aquatic life and should consider not having aquatic life as a pet. Go to cdc.gov/healthypets for more information about aquatic life and disease.
The information on this care sheet is not a substitute for veterinary care. If you need additional information, please contact your veterinarian as appropriate.
Health & Wellbeing
Good morning, How do I use the acclimation guide for pond fish? If i quarantine them for 2 weeks how do I introduce them to the actual pond they will live in? Thank you
The majority of the acclimation guide is intended for introducing animals recently purchased online into a quarantine environment that have been inside a dark box for 24+ hours and the water quality is most likely degraded from waste. Hopefully you followed these steps before introducing your pond animals into their quarantine environment. After the quarantine period the acclimation from this environment should be relatively easy and quick – given the water parameters in the quarantine environment are ideal and similar to your pond. The best way to move the fish would be to put them in a 5 gal. bucket and float the bucket in the pond for at least 30 minutes so the temperature in the bucket can gradually reach the same temperature as the pond. Make sure you do this in a shady spot of the pond or during a time period when the bucket will not be in the sun. In order to keep the bucket from tipping it may take some creativity but it may be as simple as using a wooden pole laid across the
Updated on September 24th, 2025
Health & Wellbeing
Going to be bringing a few guppies home, probably all females for simplicity sake. We have the 10 gallon tank, master test kit, heater, filter, some Omega One guppy food, and the proper decorations. But I would like to know any tips on how to safely
Thanks for reaching out. the ride home should not be too difficult but when introducing to the tank, equilibrate water temperatures first by placing the bag in the tank for 15-20 minutes. Then pour out 1/2 of bag water in the sink, then add that volume of tank water to the bag. Allow to stand for 10-15 minutes. The scoop out fish and add to tank. Don't pour bag water into tank and if parasites in water, will add more of them to tank. Finish cycling tank prior to getting fish. Good luck.
Updated on September 24th, 2025
Health & Wellbeing
I got 3 zebra danios and 2 leopard danios at petco and in about a day of having them one died. the next day another dies with a strange white spot growing on it. it was not like cotton through which I hear is a disease. my tank is a 20 gallon and be
Anytime there is an unexpected loss of fish, water chemistry should be checked. Use a home test kit ( https://www.petco.com/shop/en/petcostore/product/api-freshwater-master-test-kit# ) or submit a water sample for testing. Most pet stores will do this for free or for a small fee. Confirm an absence ( 0 ppm ) of ammonia and nitrites with a nitrate level of 20 ppm. pH can range between 6.5 and 8, water temp should be 65 F to 75 F. If chemistry and water quality are within normal parameters, then illness or aggression would be other reasons for the loss. It is always recommended to quarantine fish in a separate tank for 2-4 weeks prior to adding them to the main tank. During this time, they can be treating for infection or parasites. I am sorry for the loss of your fish.
Updated on September 24th, 2025
Health & Wellbeing
I just got a good fish today and it died why is that
The most common cause of death of a newly acquired fish is usually shock or incorrect water quality. Fish tanks should be set up and left running without fish for at least 3-4 weeks to establish a proper nitrogen cycle. There are products that can shorten this time period. If this is not done, there may be high levels of ammonia, chloramine, nitrates and nitrites which can kill a fish. When introducing a fish, the bag should be floated in the tank for about 30 minutes to acclimate the fish to water temperature. This can prevent shock if the water is too hot or too cold. Test your water quality with a home test kit or submit a sample for testing. Most pet stores or aquarists will do this for free or for a nominal fee. Correct any imbalances as indicated. Slowly acclimate any new fish as written above. You can request a consultation to discuss your concerns in greater detail if necessary. Buying fish and starting a tank can be quite confusing initially.
Updated on September 24th, 2025
Health & Wellbeing
Hello, I was wondering how one would introduce new fish to a aquarium that already has preexisting fish. Whenever I add new koi fish to my collection, most if not all of my old koi fish die from diseases. Can you explain how this process could be don
Ideally you would quarantine any new Fish in a separate aquarium for a few weeks to make sure they do not show any signs of diseases or infection. Once 2-3 weeks have passed without any signs of a problem then it is usually pretty safe to introduce to the common aquarium. Good luck and I hope they do well!
Updated on September 24th, 2025
Health & Wellbeing
We have added fish to our newly set up aquarium twice now and both times the fish were dead or dying within 24 hours. The pH is at the proper level. The tank was filled with spring water. Why do our fish keep dying?
It is possible the tank has not cycled properly which results in high ammonia and nitrite levels which can kill fish.
Allow the tank to run, without fish, for at least 4-6 weeks. During this time, use a home test kit or submit a water sample for testing every few days. The local Petco may do this for free or for a small fee.
What you are looking for is to have ammonia and nitrites at 0 ppm and nitrates at 20ppm or less. pH can hover around 7 for most community fish. Avoid large, rapid swings in pH though. What is happening in the tank during this time is that beneficial bacteria are populating the gravel/substrate and the filter. These bacterial populations are responsible for the Nitrogen Cycle. This cycle breaks down wastes from fish, uneaten food and plant matter into by-products that are filtered out or dissipate. You can "cycle" a tank with fish, however this increases the risk of loss.
Once your tank has cycled, you can add fish. You will still need to monitor water chemistry a
Updated on September 24th, 2025
Health & Wellbeing
Hello! Things didn’t go so well with cichlids and I only have one remaining which I moved to a different tank. The 45 is now empty and the others besides one blue African cichlid has died. I did water tests and most came out fine except the Carbonate
Water conditioning can be complicated and I recommend to stop by your local aquarium store. They are most often familiar with the local water quality and can give recommendations specific to your location. Some areas need buffering solutions to help control things like the water pH. Here are a few links which may help answer some of your questions about water condition: https://www.aqueon.com/articles/freshwater-aquarium-water-quality https://www.petcoach.co/article/aquarium-water-management-alkalinity-vs-water-hardness/ Before moving your goldfish, make sure all the conditions are appropriate for goldfish: https://www.aqueon.com/information/care-sheets/goldfish https://www.petcoach.co/article/how-to-help-your-new-goldfish-thrive/ I hope this helps and please feel free to post any additional questions.
Updated on September 24th, 2025
Health & Wellbeing
I would like to know how I can make my goldfish live the longest possible life they can and how to add more decor after I added the water and conditioning today and I am going to go get my fishies I think I am going to go with two but how to properly
Gold fish can make great fish but they can live up to 25 years and require a large tank that may need to be upgraded if they grow too large. Do get at least 2 fish. Here are some links which may help: https://www.petcoach.co/article/chewing-in-puppies-how-to-control-it/ https://www.aqueon.com/information/care-sheets/goldfish https://www.hartz.com/how-to-introduce-new-fish-into-your-aquarium-tank/ I hope this helps and congrats on your new pets!
Updated on September 24th, 2025
Health & Wellbeing
I changed my goldfish to new tank, and now he's staying on the bottom and not swimming around. When I go up to the tank he try's to move around. It's like he can't swim
Hi there, when you change a tank over you should take some water from the previous tank then make it up with freshwater. You should let this stabilise for one week before adding the fish. If you put a fish straight into a new tank without letting the water acclimitise it can be a shock to it's system. At this point all you can really do is let the fish settle in and don't disturb its tank for a week or so.
Updated on September 24th, 2025
Health & Wellbeing
We bought my son 5 cherry barbs earlier today along with a tank rocks and some items for the fish to hide in. About 9:30 tonight we checked on the fish and unfortunately they had all died. We followed YouTube videos and read articles about how to tra
I'm sorry for the loss of your fish. If the tank was a "new" tank, it likely was not sufficiently cycled. The fish may have died after being exposed to high levels of ammonia or nitrites.
A fish tank should be cycled for 4-6 weeks before fish are added. This allows time for beneficial bacteria to populate the filter and substrate. These bacteria are responsible for breaking down wastes (fish waste, decaying plants, uneaten food) to prevent a buildup of ammonia, nitrites and nitrates.
A tank can be cycled with fish, however this requires close monitoring of water chemistry and frequent partial water changes to stabilize chemistry and maintain water quality. Cycling with fish increases the risk of fish loss.
Updated on September 24th, 2025
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