How to Make Rocks Safe for Aquarium Fish

Rocks can enhance an aquarium's appearance.

Rocks can enhance an aquarium's appearance.

Most fish thrive in environments that mimic their natural environment, and rocks and similar tank decorations can provide your fish with a sense of security. However, rocks removed from the wild may contain bacteria and parasites that could harm your fish, so it's important to thoroughly clean them.

Ensure that the rocks you've selected will work well with your setup by consulting care guidelines for your fish. Some fish, for example, should not have access to small gravel, which they may eat and choke on. Some rocks can raise or lower the pH of your aquarium, so research the rocks you've chosen before trying to use them in your tank. Generally speaking, rocks such as quartz and basalt are safe for most aquariums.

Wash the rocks in hot water and scrub the crevices with a toothbrush or other small, soft brush. This will remove any dirt and debris that could cloud your aquarium and will prevent worms, bugs and other foreign organisms from infecting your aquarium.

Place the rock in a bucket containing a water sample from your aquarium for 24 hours. If the rock does not crumble, it is usually safe to use. Check the pH of the water in the bucket using a pH test strip to ensure the rock is not radically elevating or lowering the pH. If it is, it may cause problems with your aquarium chemistry and you should not use it.

Items you will need

  • Toothbrush
  • Bucket
  • PH test strips


  • Avoid rocks containing calcium and magnesium. These can cause problems with aquarium chemistry and may make fish ill. Pyrite -- also called fool's gold -- is also unsafe.

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About the Author

Brenna Davis is a professional writer who covers parenting, pets, health and legal topics. Her articles have appeared in a variety of newspapers and magazines as well as on websites. She is a court-appointed special advocate and is certified in crisis counseling and child and infant nutrition. She holds degrees in developmental psychology and philosophy from Georgia State University.

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