Big pieces of carbon will be much less effective than an equal quantity of smaller pieces---less surface area. I prefer Chemi-Pure, a carbon based product that comes in its own bag, Reasonably priced, especially when you buy online in quantity, and it lasts about 6 months. IMO, most of the carbon (not made by major aquarium supply companies) is worthless. Not just any carbon is good for hobbiest use. If its shiny, it fits the "worthless catagory".