Float the bag in the water for 15-30 minutes. Your fish likely came in a bag from a pet store. If your fish did not come in a bag, you can transfer the fish and water to a small, plastic bag. Tie the end of the bag together and use a rubber band to seal the bag. It's important the bag is sealed tight, as your want your fish to stay in its original water for the initial 15-30 minutes minutes.
Cut open the bag. Cut it just under the metal clip or rubber band keeping the bag closed. Roll down the top edges of the bag about an inch. This will create an air pocket. This pocket will allow the bag to float as you begin adding water from the tank to the bag.
Add water from the tank every 4 minutes. Once again, you will add half a cup of water to the bag every 4 minutes. Keep adding water from the tank until the bag is full.
Gather your supplies. For more sensitive fish, such as shrimp and sea stars, you may have to use the drip method. With the drip method, you set up a series of tubes running from the main tank to a bucket of water. You will need the following to use the drip method:
Float the fish initially. Fill the buckets a little under halfway full with clean aquarium water. You will need to start off by floating the fish to acclimate it to the water in the buckets.
Transfer water to the bucket. Gently lift up the bag. Pour the contents of the bag, including your fish, into the water.
Set up a siphon drip. Place one end of the airline tube in the aquarium. You should also tie several very loose knots in the tubing. This will help regulate the flow of water and air. You want to get a rate of 2 or 4 drips per second.
Discard half the water once the water doubles. It may take awhile for the water in the bucket to double, so be patient. In general, it takes about an hour. As soon as the water doubles, carefully discard half the water. You may have to scoop out the water using a cup or smaller bucket to avoid dumping your fish.
Transfer your fish to the main tank. Use a bag to gently scoop out your fish. Gently pour the contents of the bag into the main aquarium.
Get your tank. A quarantine tank is important as it keeps a fish away from the rest of your aquarium. It is highly recommended you use a quarantine tank before acclimating your fish to your main aquarium. If a fish you just bought is sick, you do not want the infection to spread to the rest of your tank. After buying a new fish, purchase another tank to use as a quarantine tank.
Install a filtration system. As with a regular aquarium, your quarantine tank should have some kind of filtration system. This will keep your fish safe and healthy during the quarantine period.
Add a heater. This will keep the water at a safe temperature for your fish. You should also get a thermometer to record the temperature. You want to make sure the temperature is safe before transferring your fish to the quarantine tank.
Fill the aquarium with water from your main tank. The quarantine tank should be similar to your regular tank. Once your fish is ready to be transferred to the regular tank, you want the transition to be as smooth as possible.
Monitor your fish for 2 to 3 weeks in the quarantine tank. Watch your fish closely during this time. Before introducing a fish to a tank of other aquatic life, you want to make sure it does not have any diseases. Diseases can spread fast in a fish tank.
Repeat the floating process to transfer the fish to the regular tank. If two to three weeks pass without incident, you can transfer your fish to the regular tank. You would repeat the same floating process you used to acclimate your fish to the quarantine tank.