Rocks are a nice addition to most aquariums and even fish species that do not hail from rocky environments can appreciate the sheltered areas offered by a rocky set up. If you keep rock-dwellers, such as the fascinating Mbuna cichlids from Lake Malawi, rocks are more or less mandatory. In addition to natural rocks, it is possible to furnish your aquariums with your own home-made rocks. By forming your own rocks at home you can tailor your aquarium setup down to the smallest details.
To make your own rocks, you will need Portland cement and play sand. Portland cement is one of the most commonly use types of cement so it shouldn’t be hard to obtain. It consists chiefly of different calcium silicates, but is usually also filled with clinker phases that can contain iron, aluminum and magnesium. Portland cement is considered safe for aquarium use as long as you get your cement from a reputable producer that adheres to the official cement standards. Portland cement is sold as a powder and will turn into a paste when you mix it with water. As the reaction between cement and water progresses further the paste eventually turns into a solid “rock”. Type 3 Portland cement is recommended, but type 1 or type 2 will also work.
- Wash the play sand. (This step is not mandatory but will yield stronger rocks.)
- Mix one part Portland cement with four parts play sand. The result should be pasty and you should be able to form balls in your hand. Always use durable rubber glows to prevent alkali burns!
- Place damp sand in a container and dig out hole of suitable sizes and shapes – you have now created a mold.
- Drop the cement mixture into the mold and shape it.
- If you want to form caves, tunnels, holes etcetera, use more damp sand.
- Leave to rest for at least 24 hours.
- Cement is too alkaline even for fishes known to love a high pH-value and must therefore always be cured before being placed in the aquarium. Cure your home-made rocks by placing them in a bucket of water for at least three days. Frequently change the water in the bucket. If your fish prefer a lower pH-value, cure the rocks for three weeks. Adding something acidic, such as vinegar, can speed up the curing process. Always check the pH-value of the water in the bucket before you decide to add the stones to your aquarium.
Alkaline burns
Cement is very alkaline (pH 12 to 13) and can cause serious skin injury. It is therefore important to use durable rubber glows and long sleeved clothing when dealing with cement. If you spill anything onto your skin, you should brush of any powder and then flush the skin with clean running water for at least 20 minutes. If possible, add something acidic such as vinegar or lemon juice to help neutralize the alkalinity. After using acidic liquid, it is a good idea to wash it away with milk to prevent the risk of acid-burning. (If you can see ulcers, never use anything else than ordinary water to rinse the wound. The risk of spreading infection to the wound is too severe.) Do NOT wash alkali burns with alkaline soap.
Seek medical attention and inform the medical personnel that you have been exposed to cement and should be treated for alkali burns. Always seek medical attention right away, because alkalis will continue to destroy tissue for a long time. It is possible to have wet concrete on your skin for several hours without feeling any discomfort while the alkali is gradually destroying your skin microscopically.
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