I believe one 6.5 oz bag is good for you to 40 gallons. They do sell larger bags (11oz and 46.9oz) so you can kinda do some math and figure out what works best for your set up. hope that helps
According to boomer, CPE is basically medium grade GAC, GFO, sprinkled with resins that don't work in salt water.
Easy for using in a space limited nano tank.
But there are cheaper more efficient routes for a larger tank.