all I know about aragonite sand is it's mainly used in saltwater tank and for fish that require a soft bed
http://www.bigalsonline.com/BigAlsUS/ct ... grande20lb
that link may be a better bet for you
sand also should be the top layer of other substrates for it to really work well...also sand will compact so it need more vacuuming (though I frown upon this)...best to keep with a gravel substrate yet a smaller size gravel; gravel comes in various colors if this is your concern
look online, you are bound to find the gravel you want...here are a list of online fish stores:
That Fish Place
Take your pick...I am sure someone here in this forum who actually dealt with sand in their tank will supply more information.