Anyone been to some of the LFS's around here and seen 50lb sacks of sand in white bean bag like bags? They're usually magic markered with a number on them to tell what grain size it is and usually sells for $30-$35 per 50lb bag. Anyone know what kind of sand this is? Strictly Fish in Long Beach has'em and Carson Tropical in Hawaiian Gardens has them as well. Just wondering if it's safe to use.