There doesnt seem to be many options for media choice. All of the retailers in Canada tend to sell ARM and ARM only. So there is course and fine. If you have a downflow style you might want to use course as fine tends to compact and restrict flow more as it dissolves. If you have an upflow style you can use either.
This is also an economical choice over fine ARM media and only costs about half as much:
Caribsea Florida Crushed Coral Substrate - 15 lbs
http://www.jlaquatics.com/product/cs...-+15+lbs..html
Edit: Not meaning to hijack but I'd love to hear about some other options.