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Adding Outdoor Wood and Rocks in Aquariums

While on a hike or walking your dog, you happen to notice this amazing looking rock or piece of wood. You think to yourself that it would look great in your aquarium, but is it safe? That’s a tough question and one that we are going to take a deeper dive into! It is important to remember that when you introduce an item from nature, it can bring algae, parasites and other microorganisms in addition to some type of chemical composition and characteristics that could potentially swing your water parameters. Never introduce rocks or wood found outside without thoroughly cleaning, treating and testing them to make sure they are safe! Remember, before you remove any items from their natural environment, be sure it is legal to do so and you are not disturbing nature.

Cleaning Rocks

To clean, you need to thoroughly rinse rocks with pressurized water, then scrub with a tough bristled brush to remove any foreign growth. You can give the rocks an Epson salt soak in warm water with vinegar to kill any potential parasites. Boiling rocks, while the most efficient, should be done with extreme caution. Though rare, rocks that are porous could contain air pockets and explode when pressure rises during boiling. Once cleaned, we can now check to see if the rocks are safe to introduce to your aquarium.

Testing Décor

Testing your newly found treasure is critical to ensuring that it is safe for your fishy friends. Some rocks contain calcium which can cause a rise in pH, making the water unsafe for some aquatic life.  To perform this test, get a bucket or tub and fill with the source water for your tank, add any chemicals to the water you would normally add. Test the water’s pH, hardness, nitrite, nitrate and ammonia. Place the décor in the water and let it soak for a few days to a week, then test the water again. If no changes happened from the first test, these are safe to add to your aquarium! There is also quick test that can be performed utilizing vinegar. If the rock starts to fizz after putting a few drops on it, this can indicate the rock contains calcite or limestone.

Cleaning Driftwood  

To clean driftwood, you need to thoroughly rinse it with pressurized water, then scrub with a tough bristled brush to remove any foreign growth. Boil for 30 minutes if possible, if not, soak in very hot water in a bucket. Allow driftwood to soak for 24 hours and check to see how much tannins it releases, if this is an acceptable amount, soak in clean water for another 24 hours. If releasing too many tannins, continue to soak, changing the water every 48 hours until the tannins color is desirable.

Now that you have cleaned and tested your new natural décor, you can add this touch of nature to your aquarium giving it that realistic feel you will love, and your aquatic life will appreciate!

Known Safe Rocks

  • Granite – While safe, it is extremely heavy.
  • Holey Rock
  • Lava rock – Not safe to boil!
  • Onyx
  • Pumice – Not safe to boil!
  • Quartz – Ensure the stone is smooth.
  • Slate – Ensure the stone is smooth.

Known Unsafe Rocks

  • Amethyst (it contains Manganese and unchelated iron),
  • Dead Coral pieces or coral sand – Okay for Marine Tanks.
  • Geodes
  • Ironstone
  • Limestone
  • Marble
  • Tufa rock - This a porous limestone rock. Although not safe for most freshwater aquariums, it is safe to use for Marine aquariums or African cichlid species only tanks where you are looking for an elevated pH level.

Store-bought Decor

For store-bought driftwood and rocks, it’s still important to wash them thoroughly to remove any dirt, dust or foreign particles that may be present. Soaking store-bought driftwood before placing in your aquarium will also let you know how much tannins it will be releasing into your tank. Tannins are beneficial for fish but turn your tank water a tint of brown; however, soaking for a long period of time can help reduce this effect.

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Reviewed by Don Spaeth, Petco’s National Aquatic Care, Education and Programs Manager

Don is Petco’s National Aquatic Care, Education and Programs Manager. He is an avid aquarist who has worked with and cared for freshwater and marine aquatic life for over 40 years. Throughout his 27+ years with Petco, Don has actively been involved with our aquatic vendor partners and worked to promote aquatic education both in store and company-wide.