How to Acclimate New Fish to Your Home Aquarium

It’s always exciting to purchase new fish at the pet store to add to your home aquarium. Unfortunately, it’s quite common for fish to die shortly after being brought to their new home from the pet store. While many new fish owners are quick to blame the pet store for selling fish in poor health, in reality, this untimely passing is often the result of budding aquarists not knowing how to acclimate aquarium fish to their home aquariums properly.

Many people mistakenly equalize the temperature by floating the bag in the tank and then pouring both the fish and the water into their aquariums. This practice is ineffective for acclimating fish and risky, as pet store water may introduce diseases or parasites into your home aquarium. Water from the pet store can contain diseases and parasites that will be transferred to your beautiful community tank at home.

A slow, careful acclimatization process will give your new fish the best chance for survival in your tank, although it will not protect your other fish from any diseases or parasites that the new fish may be carrying. Here’s the right way to acclimate fish to their new home.

How to Add New Fish to an Aquarium

1. Open the Bag

   When you get your new fish home, turn down the lights to avoid shocking your new pet. Your next step should be to take off the rubber band and open the bag. Place the bag in the tank, so the water supports it. Next, roll the open top of the bag down four or five turns, so it creates a ring of air trapped in the rolls of the plastic bag. Now the bag will float on its own without tipping over. If it is still unstable, a couple more rolls might be needed.

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2. Add Water From the Tank to the New Bag

   Acclimating is a slow, steady process. To begin, dip one-half cup of tank water from the tank and add it to the bag. Now wait 15 minutes and do it again. This slow process will allow your new pet to acclimatize to a change in pH and temperature as well as new nutrient levels, oxygen content, salinity, sounds, and lighting.

3. Check Water Quality

   Check the water quality in your aquarium to ensure it is appropriate for the fish. You should test the ammonia, nitrite, nitrate, hardness, alkalinity, pH, and temperature regularly. You should only think about adding new fish to your aquarium when all of the water quality parameters are at the correct levels.

   Tip

   Adding new fish into the aquarium will increase the bioload on the filter system, so only a few new fish should be added to the aquarium at a time. This allows the beneficial bacteria in the biofilter to grow enough to remove the additional ammonia waste the new fish produce before it can build up to toxic levels. Adding many fish at once can overload the biofilter and cause fish loss from ammonia increases.

4. Test the pH

   To avoid pH (acid/base balance) shock, while the temperature is equalizing, you need to test the pH of the water in the bag and compare it to the pH of your home tank water. In most cases, for a short trip of an hour or less from the pet store to your home, there will be little change in the water quality in the transport bag. For long trips, such as when the fish are shipped from the breeding farm through the distributor and then to the pet store, the fish may be in the bag for over 24 hours and up to a few days. In these cases, the pH of the water will drop because of the fish’s respiration, and the ammonia level in the water will increase.

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5. Address pH Imbalances As Needed

   If the pH difference is less than 0.4 units, you can add the fish after the initial water mixing and once temperatures have equilibrated. For a larger pH difference, such as 1.0 unit or more, gradually add more tank water to the bag until the pH levels match. The measure of pH is exponential, so a difference of one unit on the pH scale is 10 times the level of acidity between the two water samples being tested. Discus fish are a prime example of a fish species that need a long acclimatizing period because they require a lower pH (more acidic) water than most other fish species.

6. Add the Fish to the Aquarium

   Once the temperature and pH of the water in the bag are similar to the water in the aquarium, remove the fish bag from the tank and use a net to take the fish out of the bag. Add the fish into the aquarium carefully, ensuring that their fins do not get caught in the net mesh.

   Warning

   Do not pour the water from the bag into the aquarium; simply discard it. If removing the bag and its water decreases the level of water in your aquarium, add fresh dechlorinated water to the top of the tank level.

7. Monitor the Fish for Bullying

   It is important to observe your new fish to be sure they are not being picked on by other fish in the aquarium. It is also helpful to feed your fish a small amount of food at this time so that the current fish are busy eating and less likely to bother the new fish while they settle in. Remember, it is always better to place new fish into a quarantine tank for two to four weeks before adding them to the main aquarium with your other fish. Use this same technique for introducing the new fish into your filtered quarantine tank.

Preventing Problems With Your Fish During Acclimation

More new fish have been killed by pH shock than from any other problem after adding them to an aquarium. Differences in pH, while they may not sound significant, can be lethal to a fish. In fact, as little as a 1.0 difference can send your fish into pH shock. This is something they may recover from, or may not, depending on the severity of the difference in pHs. The bigger the difference, the more chance of your new fish dying from it.

Try to learn what the proper pH is for your fish species (most are in the 7.0 to 8.0 range, but some like higher levels and some lower). Also, over time, the pH in the water will naturally drop due to acids produced by fish metabolism. Regularly performed water changes (25% or more per month) will keep the pH more stable and replenish the alkalinity (pH buffering) in the water. If your local water supply is soft (low alkalinity and hardness) you may need to add an alkalinity buffer into the aquarium water periodically to maintain the proper pH for your fish.