AquaEL Basalt Gravel 2-4mm 2kg is a natural aquarium substrate made from crushed basalt. The particles range in size from 2 to 4mm and the package contains 2kg of the gravel. The dark grey colour of the substrate provides a natural look for aquariums and is suitable for all types of fish, plants and invertebrates. The texture of the substrate helps to anchor plant roots and provide a natural environment for microorganisms to thrive. The gravel also helps to keep the water soft and clean, while promoting the growth of beneficial bacteria.