No, sorry, you received wrong information.
Grit: Small pieces of sharp stone, often granite, processed for size, Chick and Adult. All fowl need grit to break down food that goes directly from the mouth to the crop and into the gizzard. Grit is needed to process any food that your chickens eat, other than their feed, crumbles or pellets. If your chickens free range and you have any gravel, sand, or small rocks on your property they will swallow them while they are outside. Depending on the amount of gravel available, or if you keep your chicks inside additional grit should be added to their feed or provided in a separate dish. From the time that a chick starts eating anything other than their crumble feed you should add grit in an amount that is equal to salt on your food. Just a sprinkle when filling the feeder. Chicks get the chick size, and around 16 weeks can handle the adult (also may be labeled "Layer" ) size.
If the pebbles in your coop area are rounded they will not help with the break down of food, they need sharp edged stone.
Calcium: When a female chick, (pullet), reaches the point of lay (POL), any time after 16 weeks for some breeds and up to 30 weeks for some, she needs calcium added to her diet to help with healthy shell production. Calcium is usually added by providing ground oyster shell. Around 16 weeks is when most change their feed from starter or grower to layer and add calcium to the diet. It can be added to their feed or provided in a separate dish. Another way to add calcium is to rinse, heat and grind egg shells and add them to their feed. One ratio that I have seen is 4-5 eggshells = 1 healthy eggshell.
Note: Chicks should not be given additional calcium as it can damage growing organs.
