sorry, I'm stuck on "fine gravel for feeding to birds" I've got to know, why were you feeding birds gravel?I set up my first saltwater tank around 1972. It was a ten gallon with real wood trim, held together with pin nails. The only substrate available was fine gravel for feeding to birds. Filtration was an inside box filter. Decoration was a coral skeleton and giant conch shell. On top was a clear plastic canopy and a metal incandescent strip light. Bags of salt were not available yet, so the owner of the store had a garbage can with the salt in it. She weighed out how much you needed.