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Aquatic Life Acclimation Guide

Aquatic Life Acclimation Guide

Fish are sensitive to rapid changes in their environment. The water that your fish are packaged in most likely has different water parameters than that of your home aquarium. For this reason, proper acclimation is vital when introducing new fish into your aquarium. Acclimation helps your aquatic life adjust to the new 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, go to and download your free Aquatic Success Kit.

Needed supplies:

You need very little to complete the acclimation process:

  • Scissors
  • Bucket
  • Algae clip
  • Measuring cup
  • Watch or timer
  • Towel, to wipe up any spills

The steps:

Following are the steps to acclimate your new fish:

  1. Turn off all aquarium lights to reduce stress on aquatic life.
  2. Thoroughly wash your hands to remove perfumes, lotions, etc.
  3. 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. (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 air pocket 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 your aquatic life.
  8. Re-float the bag in the aquarium and slowly add ¼ to ½ cup of aquarium water to the bag every five minutes until the bag is full (see 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 your aquatic life (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.

Important details:

  • 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 airstone into the bag when acclimating your new aquatic life. An airstone 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 for 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 invertebrates 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 provides 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.
  • 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 (available at your Petco store) 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. To learn more, go to and download your free Aquatic Success Kit.

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