Typically, the younger the tank - the lesser the food. But with snails, they seem to be survivors. At least for me they have. They at times seem to go dormant only to reawaken and go crazy feeding. Two isn’t bad to start with. I also see you have lots of green on your rock. Do you know exactly what it is? Looks like days and days of food for two snails. And something you’ll want to get under control sometime soon.