Aragocrete - Artificial Rocks to Use in Marine Aquarium

Artificial rocks are used in minireefs, they act as a natural biological filter and provide habitat for fish and invertebrates.

Most aquaculturists still use wild rocks harvasted directly from the ocean, which can be harmfull to the wild reefs. Using artificial rocks you help protect the real reefs.

Artificial rocks can recreate an reef that can be home for your aquarium inhabitants. When correctly cured they are completely safe to use in aquariums.

Step 1: Ingredients

- White cement

- Coral sand (replicate sea reefs)

- Crushed oyster shell (replicate sea reefs)

- Rock salt (is like kitchen salt but with bigger crystals, in contact with water dissolves and leaves small air pockets on the rock, making it more porous)

- Perlite (vulcanic rock with tiny airbubbles trapped inside, making the rock less dense)

- Water

Step 2: Ingredient Volume Ratio

Depending on what type of rock you want to make you should use diferent ratios of ingredients. These are some of the formulas that I used.

Step 3: Making the Rocks

1- Start by making the mold using humid coral sand, you can make it in any size or shape but bigger rocks will take longer to mature/cure. Note: smaller grain size is easier to shape

2- Mix the dry ingredients until the mixture is homogeneous

3- Add water in small portions,until the aragocrete is wet enough to stay together when squeezed

4- Pour the mix in the mold, and cover with coral sand

5- Wait for the aragocrete to dry, it should take one to two days, depending on the size.

Step 4: IMPORTANT: Curing the Rocks

IMPORTANT: Don't add the rocks directly to the aquarium without being cured, these types of rocks can release deadly compounds to your fish or coral.

Curing is needed due to some components reaction with water. Organic compounds (crushed oyster & coral sand) tend to have decaying biological components attached to them, which are released upon first contact with water.

When placed inside water for the first time, cement will release phosphates and unreacted lime (calcium containing inorganic materials), which will quickly raise pH, salinity and electrical conductivity of the water, making it unsuitable for some living organisms.

The rocks I made were curing in 16 liters (4,2 gal) containers for 8 weeks (60 days). One week after the rocks were placed in water the pH raised from 5 to 12. At the end of the 60 days, no rock formwas fit for aquarium placement because the water pH was around 10 which is higher than optimal (around 8.0 - 8.3), this means rocks will have to cure further.

This happened due to only changing the water weekly, as it should be changed daily for 60 days preventing the water from saturate.