I was at lfs today looking at biorings to put in my cascade 1000 cannister filter once I get it to finish this cycle. They have 750 gm, and 500 gm. The 500gm are bigger, where as the 750 are octagon shaped and smaller. Does it matter which one? Do they both offer the same surface area? Also, they come in a plastic bag. Should I put in a nylon bag before putting into the filter? Or let lay freely? And how much is too much? The box didn't say what gallon tank they were for but the aqua clear that was much smaller quantity said for 50 gal. Mine is 46.