How to Clean Algae off Decorative Aquarium Rocks

Algae should wipe easily off your tank decorations.

Algae should wipe easily off your tank decorations.

That icky stuff growing on your decorative aquarium rocks detracts from your underwater interior design. Algae is easy to clean off; correcting the factors that promoted the growth in the first place is more important and requires a bit more effort, but it prevents algae from just coming right back.

Cleaning the Rocks

Remove the decorative rocks from your aquarium.

Hold the decorative rocks under hot running water and scrub them thoroughly with a toothbrush or soft sponge. Get into all the cracks and crevices, which is usually easier if you use a toothbrush. Subsequent use of the toothbrush for your own dental hygiene purposes is not advised.

Fill a large bucket or container with hot water if you can't remove all the algae with good old-fashioned elbow grease. It should be big enough and have enough water to fully submerge your tank decorations. Add in 1/2 cup of bleach per gallon of water.

Soak your decorative aquarium rocks in bleach water for 10 to 20 minutes, until you see the algae floating off.

Take the fake rocks out of the bleach water and rub them down with a toothbrush or soft sponge under running water. Rinse them thoroughly.

Preventing Regrowth

Turn your tank light off for 16 to 18 hours per day and don't let your aquarium receive direct sunlight. Move your tank, hang some shades, drape a towel over the tank where the sun hits it or figure out another suitable solution.

Replace fluorescent tank bulbs annually and VHO lights every six months. Their wavelengths alter over time and algae tends to spring up when they become favorable, and the growth won't like it when the wavelengths change suddenly.

Look over your filter, protein skimmer and other tank equipment every day to make sure everything's in order. Clean them out and perform any maintenance as recommended in your owner's manuals.

Replace 10 to 15 percent of your aquarium water every two weeks.

Provide aeration by hooking up a trickle filter or fountain, adding an airstone or bubble wand or using another device from your pet or fish supply store.

Test your water chemistry weekly so you know if there's any elevation in nitrate, phosphate, ammonia or other nutrients algae love to snack on. Take appropriate steps to address the particular elevation.

Remove dead fish, invertebrates or plants promptly from your watery ecosystem. They give off ammonia and other compounds that drive algae growth as they decompose.

Items you will need

  • Toothbrush or sponge
  • Bucket or other container
  • Bleach
  • Light bulbs
  • Shade or towel
  • Aerator
  • Water testing kit


  • Don't try to clean your tank decorations with a metal-tipped algae scraper, steel wool or other abrasive cleaning tools, as they'll probably scratch up the surfaces.

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About the Author

Eric Mohrman has been a freelance writer since 2007, focusing on travel, food and lifestyle stories. His creative writing is also widely published. He lives in Orlando, Florida.

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