How to Get the Hard Calcium Deposits off an Aquarium

Hard water can make your glassy cloudy, streaky and hard to see through.

Hard water can make your glassy cloudy, streaky and hard to see through.

Calcium deposits are caused by minerals in the water where your fish live. They may form into a crust or develop into streaks on the glass walls. You can remove hard deposits from your tank without putting your fish in danger with chemicals.

Fish in the Tank

Rinse your aquarium scraper with clean water so that there are no chemicals or possibly harmful dirt particles on it when you place it in your aquarium. Insert the aquarium scraper in the water. Make sure all the fish get away from the scraper and do not scrape against the tank if fish are in the immediate area of the scraper.

Scrape the walls of the tank with the moderately sharp end of the aquarium scraper to remove as much of the hard calcium from the tank walls. Use caution not to press so hard on the scraper that you damage the glass.

Observe your tank to make sure all of the calcium you have scraped off the walls of the tank gets filtered out by the tank filter. Scoop out any large pieces of calcium debris with a small net.

Fishless Tank

Remove the fish from the tank if you feel you can not remove the hard calcium deposits safely or completely without contaminating the water in the tank. Place them in a properly prepared spare aquarium while you clean the tank.

Apply a small amount of lemon juice or vinegar to a washcloth and scrub the hard calcium buildup away; use lemon juice and vinegar to clean; they are nontoxic and will not harm your fish if a small amount of residue is left after cleaning.

Rinse the tank out completely and replace the water.

Items you will need

  • Aquarium scraper
  • Vinegar or lemon juice
  • Wash rag
  • Net
  • Spare aquarium
  • Fresh water for your tank
  • Calcium test kit
  • pH test kit


  • Check the pH of the tank with a pH kit to make sure the pH is at an acceptable level for your specific type of fish. Make whatever adjustments are necessary to return the water to the appropriate pH for the specific type of fish you are keeping after you clean away the calcium. Check your calcium levels with a calcium testing kit to prevent further problems from developing.

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About the Author

Jen Davis has been writing since 2004. She has served as a newspaper reporter and her freelance articles have appeared in magazines such as "Horses Incorporated," "The Paisley Pony" and "Alabama Living." Davis earned her Bachelor of Arts in communication with a concentration in journalism from Berry College in Rome, Ga.

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