The Hugo Kamishi Red Quartz Sand is fine graded sand that ranges from 0.5-1mm in diameter. Sand can look very nice in an aquarium and it is better for fish that dig or forage in substrates. Catfish, gobies, soles, spiny eels, and cichlids are all examples of fish that manipulate the substrate. With sand, these fish can dig or ‘earth-eat’ without any risk or damage. Gravel wears down the barbels of catfish, and with spiny eels especially, skin wounds become a site for bacterial infections. Sand is mandatory for spiny eels and ‘freshwater’ soles/flatfish. The particle size of sand works better for smaller fish. Plants root very well in sand. Do not use sand with an undergravel filter. Sand is much cleaner than gravel as the space between gravel pieces is big enough to allow debris in.