I'm debating whether I should get 50lbs. of Calcium Carbonate Grit made by MICRONA. Here is the product description: "MICRONA Poultry Grit is derived from calcium carbonate. As a grit source, it is superior to oyster shell – shell is not hard enough to do the digesting task grit will. Most laying poultry will benefit from MICRONA being offered free choice. Because of it’s pH adjusting qualities, MICRONA will also keep coops and runs hygienic and clean. Just sprinkle a handful per square foot, then spread your bedding material. MICRONA Poultry Grit 6 x 10" My ducks are at 20 weeks now and I will be switching them over to layer feed this week. Is Calcium Carbonate safe for ducks? (I don't see why not...but...just checking....) Thanks!