You just got a new fish and can’t wait to take it home and see it in your aquarium? Before you do anything, you need to know how to acclimate your fish and take the proper steps.

Acclimating a fish is a bit more complicated than just throwing it into the tank; fish are easily stressed by sudden environmental changes; many will go into shock and even die if not introduced into the aquarium properly.

Because of this, a proper acclimation process needs to be gradual and prepared ahead of time. Here’s how to do it.

Step 1 – Prepare a hiding spot 

Once you’re ready to introduce your fish to its new home, prepare a hiding spot for it inside the tank. This could be a rock, a piece of driftwood, or a simple aquarium ornament. A hiding spot will help reduce stress and gives your new fish a “safe place” in a frightening new environment – and will allow them to get used to the aquarium gradually. If you already have fish, a hiding spot  can also prevent them from bullying their new tankmates.

Step 2 – Place the bag containing your new fish into the aquarium

When buying fish in aquarium stores, they’ll generally be stored in little plastic bags. You should never empty the bag into your tank – the sudden change in water parameters can cause a lot of stress to your fish – and you could also be introducing disease and bacteria from the pet store into your aquarium.

Rinse the bag with tap water and gently place the bag into the aquarium without opening it. Because there’s always air in the bag, it will float. The temperature inside the bag will start to match the aquarium water’s temperature. This way, the fish will gradually get used to the temperature of the aquarium’s water. Wait 30 minutes.

Step 3 – Lights off

Turn the aquarium’s lights off before placing the bag into the water. Intense light can stress your fish out – note it can’t escape this light while it’s in the bag.

Step 4 – Make a small cut at the top of the bag 

While the bag is still closed, make a small incision under the top of the bag. You mustn’t cut a submerged part of the bag, only the section that is floating above the water. Fold the top edges of the bag inwards to create an air pocket. Creating this air pocket is necessary to keep the bag from sinking.

Step 5 – Slowly pour the aquarium’s water into the bag 

Your fish should have gotten used to the new water temperature by now – but things like water hardness can also stress them out. Add aquarium water through the incision you just made in the bag every 5 minutes. A general rule of thumb is to use half a cup of aquarium water. After pouring in the first half, let the bag float for 5 minutes. Then pour another half into the bag again. The goal is to keep add the aquarium’s water every 5 minutes until you have completely replaced the water and the bag is full and almost submerged.

Step 6 – Get the fish out

Now that the fish has adjusted to the aquarium’s water parameters , it’s time to let it into the water. You should be careful not to let any water from the bag into the tank – we’d recommend using a net. Gently use the net to get the fish out of the bag and into the aquarium. Once it’s in the tank, throw away the bag and drain its water.