Basic Fish CareFreshwater

Acclimating New Fish

Scene from Finding Nemo

No one wants to buy a fish only to find it dead the next morning. Many times when someone has a fish die very shortly after bringing it home it’s due to improper acclimation of the new fish. If you improperly acclimate a fish it can shock their system and stress them to the point where they die. Knowing that no one wants that, I’ll go over how to properly acclimate fish to avoid inadvertently killing your new pet. This will only be for freshwater fish acclimation, saltwater is more involved and will be covered in a later article. You might be tempted to get your new fish and add it to your fish tank as soon as possible, but you could end up dooming your fish and possibly your whole tank if you do.

Before you add a fish to your aquarium, you need to make sure it is free of disease. Visual inspection will work if the fish is showing signs of disease, but sometimes diseases don’t show right away. This is why having a quarantine tank is extremely helpful. You can learn more about quarantine tanks by following that link, but essentially it’s a separate fish tank used to house new or sick fish. The below steps can be followed when adding a fish from a fish store to either your quarantine tank or your main fish tank if you don’t have a quarantine tank.

  1. When you bring your fish from the store home, try to keep the plastic bag it’s in covered to protect it from temperature changes and also light.
  2. When you get home, you should turn off your aquarium lights. This will help keep the new fish calm and also make your existing fish less active to reduce stress to your new guy.
  3. Take the bag with the fish in it and float the bag in the tank for about 10-15 minutes to adjust the temperature of the water in the bag to match your aquarium. You shouldn’t open the bag yet.
  4. Get a large container, that hasn’t been washed with soap before, and pour the fish and bag water into the container. It should be able to hold around 2 liters of water. Make sure it has a cover or something you can put over it to prevent your fish from jumping out. Instead of a container, you could use the bag the fish came in if it’s big enough and you can keep it upright.
  5. Add about half a  cup of aquarium water to the container and continue to do so every 5 minutes or so. This helps the PH of water the fish is currently to match the PH of the aquarium water. If the PH varies too much and you skipped this step, your fish could become shocked by the sudden change. By slowly adding water, you will gradually raise or lower the PH to match.
  6. After about 30 minutes, you can add the fish to the tank. Make sure to minimize the amount of water added back into the tank by either netting the fish out, or emptying most of the water from the container. If you introduce water from the fish store into your tank, you run the risk of introducing parasites as well.
  7. Now that the fish is in the aquarium, you should leave the lights off until the next day to help reduce any stress on the fish. You also want to watch the new fish closely for any signs of disease and also aggression by other fish. New fish are more susceptible to being bullied by the existing fish in the aquarium, so you will want to keep an eye out for that and separate them in necessary. You could also rearrange decorations to help reduce aggression if you see it.

The above method is probably the best way to acclimate fish, however there are some situations where it may be best to do an abbreviated version. If you notice that the fish looks particularly stressed in the bag, either it’s breathing very rapidly or possibly not swimming and laying on it’s side, you may not want to stress it out going through the whole acclimation process. Even though going through the acclimating your fish properly is best in most situations, in this case, you may want to float the bag for a little bit and just put the fish in the tank with the lights out. I’ve even added a fish that looked particularly stressed without floating the bag and had it survive. You basically have to judge if the fish looks like it will be able to handle the acclimation, or if it would be better off just being added. In most situations, it will make sense to properly acclimate your fish though.

Thanks for reading and learning how to properly acclimate your fish to your fish tank. If you found this helpful and would like to know other tips and tricks, including the secrets many fish stores won’t tell you, please join my mailing list.


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