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SESK: Stuff Everyone Should Know · sesk.info/fish-water-change-percent

About how much tank water is a common weekly partial water change?

About 10 to 20 percent of the tank water each week.

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  1. About 10 to 20 percent ✔
  2. All of it
  3. None, just top it off

Why: A partial change removes waste without a big swing in water conditions. Small bowls without filters need changes more often.

Huh, didn't know that: Merck says small bowls and betta tanks without filters need more frequent water changes.

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References

Answer: About 10 to 20 percent. A partial change removes waste without a big swing in water conditions. Small bowls without filters need changes more often.

  1. Texas A&M Extension: Gold Rush, A Kid's Guide to Goldfish Care extension.rwfm.tamu.edu/wp-content/uploads/sites/8/2013/10/Goldrush-%E2%80%93-A-Kid%E2%80%99s-guide-To-Goldfish-Care.pdf
    Take out about 10 to 20% of the water in your tank each week
    Checked 2026-10-11.
  2. Merck Veterinary Manual (pet owner): Providing a Home for Fish www.merckvetmanual.com/all-other-pets/fish/providing-a-home-for-fish
    In small aquariums, such as goldfish bowls and betta tanks, ... more frequent water changes are needed
    Checked 2026-10-11.

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