How to Clean Hard Water Off a Fish Tank

Written by lanh ma
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How to Clean Hard Water Off a Fish Tank
Clear aquarium glass gives you a better view of what is going on in your tank. (aquarium fish 7 image by cherie from

Hard water stains are a result of a high level of calcium carbonate, also known as limestone, in the water. These stains cling to aquarium glass as a chalky white deposit, and they are often seen when the tank is drained and then left to dry. They may also be found at the waterline of a tank that is still active. While the stains are harmless, removing them adds to the visual appeal of your aquarium.

Skill level:
Moderately Easy

Things you need

  • Gloves
  • Aquarium scraper
  • Razor blade
  • Toothbrush
  • Vinegar

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    With Tank Full

  1. 1

    Put on a pair of rubber gloves. While calcium carbonate is not dangerous, you may introduce bacteria to your fish that may be harmful to them.

  2. 2

    Use a plastic scraper to scrape away at the white deposits. This method allows you to remove the offending stains without disturbing the fish.

  3. 3

    Use a new razor blade to scrape away the white stains if a plastic scraper does not get all of them.

    With Tank Empty

  1. 1

    Pour some vinegar into a cup.

  2. 2

    Swish an old toothbrush through the vinegar.

  3. 3

    Scrub at the hard water stains with the toothbrush, dipping it in vinegar again as the toothbrush dries.

  4. 4

    Allow the vinegar to sit on the hard water stains for five minutes.

  5. 5

    Rinse the aquarium thoroughly with hot water.

  6. 6

    Allow the aquarium to air dry.

  7. 7

    Inspect the aquarium and repeat Steps 3 through 6 if the stains are not gone.

Tips and warnings

  • Never use commercial glass cleaners to clean your aquarium as they can leave a residue that is harmful to your fish.

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