How to Acclimate New Aquarium Fish to Your Home Aquarium

Person holding a bag of goldfish in their palm

It's always fun to go to the pet store and buy fresh fish for your home aquarium. Unfortunately, fish sometimes perish quickly after being delivered from the pet store to their new home. While many new fish owners immediately blame the pet store for selling sick fish, this premature death is frequently the fault of inexperienced aquarists failing to properly acclimatize aquarium fish to their home aquariums.

Most people just float the bag in the tank to equalize the temperature before dumping the fish into their aquariums, water and all. Not only is this a lousy technique to acclimatize fish, but it's also a bad idea to put pet store water into your tank. Pet shop water may include illnesses and parasites that will be transmitted to your lovely communal tank at home.

Although a long, meticulous acclimation procedure will offer your the best chance of life in your tank, it will not protect your existing fish from any diseases or parasites that the may have, it will give your the best chance of survival in your tank. Here's how to properly acclimatize fish to their new environment.


Before adding new fish to a communal tank, they should be quarantined for at least two weeks. If you don't have extra tanks to quarantine them in, you'll have to keep a close eye on the fish dealer's aquariums. If any of the fish in the dealer's aquariums are ill, dead, or have ich, don't buy them and put them in your communal tank.

How to Add New Fish to an Aquarium

  1. Open the Bag

    Turn down the lights when you get your new fish home to avoid scaring your new pet. After that, you should remove the rubber band and unzip the bag. Place the bag in the tank so that it is supported by the water. Next, roll the bag's open top down four or five times to produce a ring of air trapped between the plastic bag's rolls. The bag will now float upright without tipping over. If it's still unsteady, a few additional rolls may be required.

  2. Add Water From the Tank to the New Bag

    Acclimating takes time and effort. To begin, take 1/2 cup of tank water and pour it into the bag. After 15 minutes, repeat the process. This gradual transition will help your new pet adjust to changes in pH and temperature, as well as new nutrition levels, oxygen content, salinity, noises, and illumination.

  3. Check Water Quality

    Make sure the water quality in your aquarium is suitable for the fish. Ammonia, nitrite, nitrate, hardness, alkalinity, pH, and temperature should all be tested on a regular basis. Only consider introducing additional fish to your aquarium if all of the water quality criteria are within acceptable limits.


    The bioload on the filtration system will rise when new fish are introduced to the aquarium, thus just a few new fish should be added at a time. This permits the biofilter's helpful bacteria to grow large enough to eliminate the extra ammonia waste produced by the new fish before it reaches dangerous levels. Adding a large number of fish at once can overload the biofilter, resulting in fish loss when ammonia levels rise.

  4. Test the pH

    While the temperature is equalizing, measure the pH of the water in the bag and compare it to the pH of your home tank water to avoid pH (acid/base balance) shock. In most circumstances, the water quality in the transport bag will not vary much during a short travel of an hour or less from the pet store to your home. The fish may stay in the bag for more than 24 hours and up to a few days for long excursions, such as when they are sent from the breeding farm to the distributor and then to the pet store. Because of the fish's respiration, the pH of the water will drop, and the ammonia level in the water will rise.

  5. Address pH Imbalances As Needed

    After the first water mixing and the temperatures have equilibrated, you can introduce the fish with a pH difference of less than 0.4 units. If the pH difference is greater than 1.0 unit, you'll need to add more water to the bag until the pH matches that of the tank. Because pH is measured exponentially, a one-unit difference on the pH scale equals 10 times the difference in acidity between the two water samples being analyzed. Discus fish, for example, require a longer acclimatization period than most other fish species because they demand a lower pH (more acidic) water.

  6. Add the Fish to the Aquarium

    Remove the fish bag from the tank and use a net to remove the fish once the temperature and pH of the water in the bag are identical to the water in the aquarium. Carefully place the fish in the tank, making sure their fins do not get stuck in the net mesh.


    The water from the bag should not be poured into the aquarium; instead, it should be discarded. If removing the bag and its contents lowers the amount of water in your aquarium, fill it out with fresh dechlorinated water.

  7. Monitor the Fish for Bullying

    It's crucial to keep an eye on your new fish to make sure they're not being picked on by the other fish in the tank. It's also a good idea to offer your fish a tiny quantity of food at this time so that the existing fish are occupied and less likely to harass the new fish while they adjust. Remember that new fish should always be quarantined for 2-4 weeks before being introduced to the main aquarium with your existing fish. Introduce the new fish to your filtered quarantine tank using the same method.

Preventing Problems With Your Fish During Acclimation

After being introduced to an aquarium, pH shock has killed more new fish than any other condition. While pH differences may not appear to be substantial, they can be fatal to a fish. Even a pH differential of 1.0 might cause your fish to go into shock. This is something they may or may not recover from, depending on the severity of the pH differential. The greater the difference, the more likely your new fish will perish.

Learn about the pH requirements for your fish species (most are in the 7.0 to 8.0 range, but some like higher levels and some lower). Additionally, due to acids created by fish metabolism, the pH of the water will naturally decline with time. Regular water changes (at least 25% per month) will help to maintain a stable pH and replace alkalinity (pH buffering) in the water. If the water in your area is soft (low alkalinity and hardness), you may need to add an alkalinity buffer to the aquarium water on a regular basis to keep the pH stable for your fish.


The pH of the water in the fish bag will drop and ammonia levels will rise during shipment. Making the transition to various water conditions as painless as possible for your fish can assist to decrease stress and losses. If it was a lengthy ride home from the fish store, you could even put a few crystals of ammo-lock (or another ammonia neutralizing product) inside the transport bag to detoxify any surplus ammonia.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.


"Aquarium Water Quality: pH. Florida Department of Agriculture and Consumer Services." ;