My local TSC Store sells 2 types of sand. White and black. The white stuff is what I have in the tank now, and have been using for years. Its labeled as "industrial sand" (I assume its for oil spills?). It contains very small amounts of what I think is iron (there black sand sized particles and there magnetic). 50lb bag for $10, you cant go wrong.
They also sell a black type of sand labeled as "sandblasting sand", but I question what its made of or whether its safe to use with fish. here's a link to it. They used the white sand as the pic though.
http://www.tscstores.com/50LB-ENVIROBLAST-SANDBLASTING-SAND-P4428.aspx
Your thoughts?
EDIT: "-50 Lb Enviroblast Sandblasting Sand -Please follow MSDS safety measures when using product -
Non-silica Product derived from the mineral ilmenite ore -A sub-angular product -Excellent for removing strong rust, thick paint from metal -Suggested for removing rust and paint from boats, bridges -Dark grey to dark brown in color"
^^^ its not dark grey or brown, its black. I've seen it in the store before.