I am interested in changing from black gravel to black sand. However wanted the users opinion on which is the better ones to look out for? Its for a 125l tank and wasnt sure if it was worth reusing the black gravel and mixing it with sand but think it would look a bit weird. Anyways bottom line (get the joke?) is that I want to find a variation of black sands on the market and the costs. Any advice is appreciated. Thank you.