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Aquatic Life Acclimation Guide

Developed with and approved by a qualified veterinarian.

fish in tank


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:

Table of Contents

Supplies needed to acclimate your aquatic life

You need very little to complete the acclimation process:

How to acclimate your aquatic life

Following are the steps to acclimate your new aquatic life:

  1. Turn off all aquarium lights and reduce ambient lighting to reduce stress on aquatic life
  2. Thoroughly wash your hands to remove perfumes, lotions, etc.
  3. 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
  4. 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
  5. 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
  6. Repeat step 5 every five minutes until the bag is full
  7. 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
  8. 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
  9. 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)
  10. Grasp the bottom corner of the bag and lower it into the aquarium
  11. 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)
  12. 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


It may take between 15 minutes to 1 hour to properly acclimate your aquatic life.

Additional care sheets

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 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.