Using Stones in an Aquarium

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The use of stones or rocks in an aquarium is very popular and you can buy lots of different types from your local aquarium shop. But be aware that not all rocks are suitable. Certain rocks may contain dangerous metals or minerals which will leech into the water over time and kill your aquatic animals or alter the chemistry of the water.

Aquarium shops are aware of this and sell stones which are either man-made or natural which will be 'aquarium safe'.

If collecting from the wild, avoid rocks that seem to glitter with a metallic glint as this may be metal which is dangerous to aquatic life.

One further test is to use an acid, like clear table vinegar and drip some into a small pool on the surface of the stone, leave for five minutes and see if the area has fizzed as the vinegar dissolves the stone. If it does, do not use this stone.

Preparing the Rock[edit]

  • Before you add the rock into the aquarium, please ensure you wash in boiling water to get rid of any bacteria, fungus, algae and parasites that may be present. Be very careful boiling or roasting rocks as they can explode!
  • Ensure that you do not place the rock on the base of a bare aquarium as the rock may crack or break the glass or plastic walls. Add a layer of fine sand or gravel underneath it first.
  • Be sure that the stone is embedded deeply enough in the substrate so it will not fall over, over time.

Points to Remember[edit]

  • Be aware that the stone will displace water in the tank so effectively reducing the amount of oxygenated water available for the life in your tank. Artificial rocks will be hollow and so will have much less effect on water displacement and weight.
  • Remember rocks have weight, can your furniture (and floor!) supporting the extra weight of the rocks?

Rocks to Avoid[edit]

  • Limestone, Dead Coral pieces or coral sand (unless you want to increase the GH of your water).
  • Amethyst (it contains Manganese and unchelated iron), Geodes, Gypsum, Ironstone, Nephrite, Marble, Jasper types.
  • Sandstone - can contain Feldspar (possible metals)

Rocks which may be Safe[edit]

  • Granite - entirely safe but can be very heavy so position carefully
  • Slate - edges can be sharp, ages well in aquariums
  • Lava rock - do not roast or boil as they will break down. Contains chelated iron which is used to fertilise plants
  • Quartz - can be sharp and does not age well in aquariums
  • Onyx
  • Pumice - not a real stone, actually glass, and may float due to being very porous - do not roast or boil!
  • Petrified wood - use the acid test before putting in the aquarium

Aquarium Styles[edit]


Certain species of freshwater fish need to be kept in a heavily stone based aquarium as that is their natural environment.

Some species of river loaches need smooth stone like faces to cling onto, ideal rocks for them include large pieces of slate.