I do not know much yet, so this might be a stupid question but if i give my ducks access to sand and pebbles which is abundant in my yard will they still need grit? i wont be able to free range them so i would ineed to put it in pile/a hopper in their run... also how much would say, 10 ducks need in a day/week or year? or what ever. I plan on getting kahki campbells, and is the oyster shell for grit? or calcium? do ducks need the oyster like chickens?? Thanks!