Can you use basalt sand in aquariums?

Yes, basalt sand can be used in freshwater and saltwater aquariums as a substrate. It is made from volcanic rock and is naturally dark in color. It's important to thoroughly rinse basalt sand before adding it to the aquarium, as it may have some dust and debris on it. Depending on the size and species of fish you keep, basalt sand may also be too coarse or sharp.