Is sandstone and sandcrete stone safe for aquarium use?
Natural sandstone should be safe to use in a fish tank as long as the rock does not dissolve in water. Test it by boiling for 30 minutes. If it is still hard after cooling, it should be fine in the tank. Sandcrete sounds like a man made rock made from sand and concrete. Concrete is high in lime and phosphates and must be neutralized or cured before it can be used in an aquarium. If the rock is sold for aquarium use or pond use then it has probably been treated by the manufacturer. If not, you may have to soak it for 24 hours in a 5% solution of muratic acid, rinse it well, and then soak it for 48 hours in clean fresh water. Give it a final rinse and then you can use it in your tank.
