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Are these rocks aquarium safe?


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I .. recycled .. some rocks from the beach, and dad just told me he thinks it's blue metal, he said he THINKS that is some sort of volcanic rock, but isn't positive.

I put some vinegar on it, no fizzling.. is anybody sure if they are safe?


Rocks There are two very simple ways to test rock to be sure they are safe for your aquarium. The first method uses Muriatic Acid (MA). This can be found at either a swimming pool supply store or possibly a hydroponic supply store. To test any given rock, put a few drops of MA on the rock, wait a couple of seconds and watch for bubbles. If bubbles are seen, this rock is NOT safe. Distilled white vinegar can also be used in a pinch. The MA test is more accurate though. When working with any chemical, it is a wise idea to use proper PPE such as gloves and splash proof goggles.

Conglomerates, that is rock made up of other rock, should always be avoided (They tend to look like concrete). To test a rock with either MA or the Acetic Acid in vinegar, a “fresh face” must be made. This is simple a spot where a piece of rock has been chipped or broken away. Weathered surfaces often do not react with acids.

Rocks with sharp edges should be avoided. In most cases, these edges can be smoothed with a bit of work and a good American cut mill file, readily available at your local DIY store. One must also take care, in enclosures where stone is stacked or piled, to properly secure the rock with aquarium adhesive to prevent accidental crushing deaths or breakage of the tank glass.

Please remember: “When in doubt, leave it out!” Below is a list of rocks that are safe for aquarium use.

Safe Rocks:

  • Crystalline Quartz ( also known as Rock Crystal, Amethyst, Citrine, Rose Quartz, Smokey Quartz)
  • Granite (care must be taken with granite, some forms contain high concentrations of pyrite)
  • Jade
  • Microcrystalline Quartz, also known as Quartzite and its metamorphic forms: Jasper, Agate, Chalcedony, Sard, Carnelian; Green coloration should be avoided due to presence of copper)
  • Onyx
  • Petrified Wood
  • Slate
  • Basalt
  • Porphyry
  • Schist
  • Commercially available “River Rocks”
  • Mica
  • Tapecrete or similar acrylic based concrete products, properly treated and sealed
  • Obsidian
Unsafe Rocks:
  • Coal, as a naturally occurring hydrocarbon, this rock is often contaminated with many other hydrocarbons.
  • Lava Rock, not recommended due to a multitude of sharp edges and the possibility of high sulfur and hydrocarbon concentrations
  • Coral, causes alkalinity issues
  • Dolomite, the metamorphic form of limestone
  • Fools Gold also known as pyrite (or any other rock with metallic veins--Acid Producing and even more so, often a lead hazard)
  • Any rock with a green or greenish color to it, these are most commonly contain copper)
  • Fossils, with exception to those in Slate
  • Limestone, the sedementary form of coral
  • Manufactured Quarts Crystals
  • Marble, if not sealed with a high quality aquarium safe epoxy
  • Sandstone
  • Shale as it often contains hydrocarbons that can be harmful in a captive enclosure
  • All Metamorphic and Sedimentary Rock not on the safe list

To sanitize rocks found in the outdoors, identification is a must. Many rocks contain gas pockets which can be a hazard during the sanitization process. It is suggested that each rock is thoroughly scrubbed with a stiff bristle brush and a supersaturated solution of non-iodized table salt. Once the scrubbing is complete, the rocks should be fully submersed in a large cooking pot and brought to a roiling boil for a minimum of three hours. The pot should preferably be aluminum, non-coated, and have a tight fitting lid. The process MUST be carefully watched as you will need to add more water, or even change the water as the stones simmer.

If any oily sheen, or excessive foaming is noticed during boiling, the rock should be excluded from aquarium use. It should also be mentioned here, that the risk of gas pockets causing rock to explode is very, very high and proper measures should be taken to prevent burns, scalds, and shrapnel injuries.

Once boiled, it is highly recommended that the rocks be thoroughly rinsed in tap water, then soaked a minimum of 24 hours in cold tap water treated for aquarium use. Use of a good water detoxification product, like Amquel+ or Prime should be used at twice the manufacturer suggested dosage. This will help to remove any trace elements that may be in the rock, or introduced during the boiling process.

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If in doubt put them in a small plastic containor as many rocks as possible least amount of water but cover them and do a ph and hardness test after a week and see how it goes? small changes I would say would be fine.

I agree with the others, safe

Also note that if the wood is also collected from a beach it may contain high levels of salt?


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Great, thankyou, Ray - good idea.

As for the wood, I have a piece of driftwood I have in the fish tank, I think you are supposed to boil it, but I just soaked it for like ages. These pieces were in the shrub way up the beach.

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I agree with the others, the rocks should be fine, but the timber could be of some concern. Make sure you treat the wood with everything you've got, then soak and re-soak and re-soak and re-soak again. Last thing you need is for the salt levels to rise so much that you end up with sardines rather than axies. I'd try as mich as possible to "sterilise" the wood too, boil/bleach/condys crystals... whatever you can get, seeing as the timber can harbour any number of pathogens that may become a proble for you.

Oh about the rocks too... I'd try sterilise them a little too. I had set up a tank with rocks out of Parramatta river once. They were washed and cleaned, but the tank ended up stinking like rotten egg gas (hydrogen sulfide) which I'm sure was from some weird bacteria from the rocks. Interesting that that's exactly what some parts of Parramatta river smell like! :blink:

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