I moved them to a grower feed last week. Not sure how old now, but got them easter weekend at 1 to 2 weeks old.
I have sand in my coops, it helps to keep the floor dry. I remove the sand mixed with poop in the spring and spread it in the garden. For me is cheaper to buy a load of sand (bed of my pick up truck) that buying bags of sand. I really like the sand in the turkey pens, they are more messy than chickens.
They usually will not overeat grit - sand in your case.
Have you been providing treats, scraps etc. for the birds as well?
I've found that food intake can vary from day to day (and week to week) depending on weather, what treats/foods I give, etc.
It sounds like they are a little over a month old so food consumption slows slightly as they get older. You switched feeds also, so sometimes it can take them a while to get used to that.