Turn off aquarium light and dim the lights in the room where you're aquarium is set up. Do this before you remove your fish from the carrying container, since fish are sensitive to light and may be traumatized by a sudden change in lighting.
Once your fish is used to the tank, you can be less strict about lighting. It's a good idea to initially introduce your fish to a dim environment, as this will reduce the shock of being introduced to a new environment.
Float the bag in the water for 15 minutes.
Simply set the bag on top of the water in the quarantine tank. The fish bag should float on the water's surface.
Set a timer for 15 minutes. Keep an eye on the bag during this time to make sure it does not fall over or come undone. For about 15 minutes, allow the bag to float. This way, the water in the bag will gradually become the same temperature as the water in the tank.
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 to the bag every 4 minutes. Get a measuring cup. Add a half cup of the aquarium water to the bag. Allow the bag to float for another 4 minutes. When 4 minutes have passed, add another half cup of aquarium water to the bag.
Keep adding water from the aquarium every 4 minutes until the bag is completely full.
How long this process will take varies. For a smaller bag, you may only need to add a couple of half cups. For a larger bag, you may need to add water 3 or 4 times before the bag is full.
Discard half the water and float the bag again. Once the bag is full, carefully lift it out of the water. Pour about half the water from the bag down the sink.
After discarding the water, place the bag back in the quarantine tank. Allow the bag to start floating again.
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.
Once again, length will vary. For a small bag, you may only need to add a couple half cups. A larger bag may need to be filled 3 or 4 times until it's full.
Release the fish into the tank. You will need a small net here. Dip your net into the bag and get your fish in the net. Gently lift the fish out of the bag and place it into the tank.
Make sure to be gentle as you net your fish. You do not want your fish to become tangled in the netting. Use a slow, swooping gesture to capture your fish.
Be gentle, but quick, when you transfer your fish to the main water. You do not want your fish to be out of water for too long.