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How to Change Fish Tank Water (Freshwater)

| Updated September 26, 2017

Things You'll Need

  • Bucket for transporting dirty water (such as a 2-gallon bucket)

  • A clean jug for pouring treated water into the tank (such as a 1-gallon jug)

  • Siphon (see photo)

  • Drops for removing chlorine/ammonia/chloramines, such as AmQuel Plus

Regular water changes are essential to maintaining a healthy aquarium. However, these water changes also need to be done properly in order to avoid harming the fish. This article outlines the basic steps that are involved in safely and easily changing out the water in your fish tank.

Every month or two, change out approximately 1/3 of your fish tank water. Changing out no more than 1/3 of the water at a time will help you avoid "shocking" the fish. If it seems like you need to change the water more frequently than every month or two, you might have a filtration problem, are over-feeding, or have more fish (or fish that are larger) than the size of the tank can handle. If you suspect a filtration problem, refer to the article down in the "Resources" section on How to Keep Your Fish Tank Clear.

Prepare to empty out the water by setting up a bucket on a towel directly in front of the tank. Have your drops ready (refer to the supplies list on the right), as well as your clean jug for transporting water back into the tank.


Then, use a siphon (see photo) to transfer water from your fish tank into the bucket. While siphoning the water, use the fat end of the siphon tube to pull excess waste out of the gravel. Push the tube into about one inch of gravel and hold it there for a couple of seconds before pulling it out and moving on to the next spot. Repeat for the entire fish-tank bottom, and try to finish before you have siphoned out the appropriate amount of water. Each time you fill up your bucket, simply pull the end of the siphon out of the tank and empty the bucket outside or in your bathtub.

Once you have siphoned out about 1/3 of the water, begin filling up the tank with fresh, treated water from your tap. If you can use a gallon jug, this will be convenient for measuring the approximate amount of drops you will need to treat it (follow the directions on the bottle). Make sure that the jug is clean and has been rinsed thoroughly (do not use a jug that previously had potentially harmful substances in it, such as chemicals). To help the drops mix, put them in before you fill up the jug with water. Also, try to get the temperature of the tap water to match the temperature of the water in your fish tank by dipping your fingertips into your fish tank before holding them under the running water as you adjust the temperature. Repeat as necessary, and then fill up your jug.

Gently and slowly empty your jug into the middle of the fish tank. Repeat with STEP 4 until your tank has been filled.


  • Never put water into your fish tank directly from the tap. Be sure that you treat the tap water with the appropriate chemical-removing drops, such as AmQuel Plus. A gallon-sized jug filled from the bathtub is a useful size for measuring the appropriate dosage (refer to the instructions on the bottle).