Pasty butt is mostly due to chilling and stress in shipment or handling, and soy based feed fed too soon. I work them into soy feeds slowly. In fact, they get no prepared feeds for the first 5 days or so. If you are seeing pasty butt in older chicks, then something else is wrong.
Chicks dont normally need grit, anyway. Grit is needed in older birds to grind grain and seeds in the crop, or gizzard. If you dont give such things to chicks, then there is little need of it.
A good age-appropriate ration fed properly will give them what they need. Avoid all the "treats" and the desire to pamper them with everything under the sun and you will solve a lot of problems. Apply the KISS principle whenever possible.
I don't give grit, in fact, until they begin to lay - then it is OS for egg shell strength. Once a bird has access to outdoors and the dirt, they get what they need in the way of gizzard grit themselves.