Add new fish to your tank slowly that it does not overwhelm them. Whether they are freshwater or saltwater fish, you will need to gently acclimate them to your aquarium.
Prepare the Water to Add New Fish to Your Tank
The water in your tank must be properly balanced. If you use tap water, you will need to treat it to remove chlorine and other things in the water. You can purchase a water conditioner at the pet store or variety store that sells pet supplies such as Wal-Mart or Kmart. It will take some time for the water conditioner to work. Read the label and follow the instructions. You cannot just pour water conditioner into the water and expect it to be ready immediately for our fish.
Feed Other Fish Before You Add New Fish to Your Tank
If you will be adding new fish to a tank that currently has fish in it, you will want to feed the fish that are already in your tank first. This will keep them happy and safe during the transfer of your new fish.
Acclimate the Temperature to Add New Fish to Your Tank
Leave your new fish in the bag that they came in. Float the bag on top of the water in your fish tank. You will want to let it float for at least one half hour. It is best to leave it floating until the water inside the bag is the same temperatures as the water in the fish tank or aquarium.
Slowly Add Water to The New Fish to Add New Fish to Your Tank
After the bag with the fish in it is the same temperature as the water in the tank, open the bag slowly and allow some tank water to go inside the bag and then reseal the bag. Every ten minutes let in more water from the tank.
After adding water three times, you can open the top of the bag and leave it open so that they bag will slowly sink and the fish can swim out into your tank. After the fish are out of the bag, remove the bag from the water.
Fish are very susceptible to shock from changing temperatures which can make them ill or kill them. If you want your new fish to survive the transfer to your tank or aquarium, you will need to gently transfer them over.