Introducing a new fish to an aquarium can be tricky. While your current pets may enjoy the environment of your fish tank, the newcomers may not. All species of fish are sensitive to sudden changes in pH value or water temperature.

In this article, we’ve outlined some of the most important things you should consider when introducing a new fish to your aquarium:

Step one: Before Acclimation

Choose your new fish carefully
Always make sure that the species of fish you’re bringing into your tank is compatible with your current fish. Nippy species don’t go well with fish with large fins; for instance, housing Tiger Barbs with your Angelfish could be a recipe for disaster. Always ask around before buying, and make sure you’re getting the right fish for your aquarium.

Ensure that your fish tank has enough plants and decorations
If your aquarium has little plants or decor, consider buying some. This will provide your new pets with a place to hide if they’re feeling stressed, or are being chased around by their new tankmates.

Consider putting your new fish in a quarantine tank
Although most aquarium owners skip this step, it needs to be mentioned. While they may appear healthy, fish from pet stores can carry a number of diseases and parasites. Some of these diseases can take weeks to show – and by the time you’ve noticed the symptoms – your other fish are likely to be infected as well. Consider setting up a “quarantine tank” that would house the new fish for three to four weeks. This would allow you to observe for (and treat) any possible illness before they are introduced to your aquarium.

Step two: The Acclimation Process

Turn off all aquarium lights
Bright lights can cause unnecessary stress to your new fish. Ideally, you want the aquarium lights to be off, and the lighting inside your room to be dimmed.

Float the bag in your aquarium for 20 minutes
Don’t open the bag yet – rinse it’s off gently with some tap water, and place it into your aquarium. This will allow your new fish to slowly acclimate to the temperature of your aquarium. Be patient and follow the acclimation process through! Not doing so can cause unnecessary stress, and even harm your new fish.

Open the bag and add some aquarium water
After 20 minutes have passed, open the bag and add a cup of aquarium water (without spilling any of its contents). This will help your fish adjust to the pH factor and other values of your aquarium. Reseal the bag and let it float for another 10 minutes.

Use a net
Never empty the contents of the bag directly into your aquarium. The water can contain snails, diseases, and various parasites. Use a net to gently transfer the fish into your aquarium. Make sure not to keep your fish out of the water for too long.

Step three: After Acclimation

Observe your new fish carefully. Are they eating? Are they swimming? Keep an eye out for any strange behavior. Even though the acclimation process lasts less than an hour, your new fish may take days, and even weeks, to get fully used to their environment.

Keep in mind that some fish may sink and appear dead immediately after the acclimation process, but be patient and follow through with all the steps mentioned above. They are very likely alive and are just stressed from a sudden change in environment.

If your new fish are being harassed

Unfortunately, this is not uncommon – especially in crowded aquariums. Some fish can perceive their new tankmates as a threat that’s encroaching on their territory – and will get aggressive. Providing plenty of hiding place for your new fish is essential.

Rearranging some decorations, or even the placement of intake/outtake valves of your aquarium filter can sometimes stop the harassment.