If you're concerned about calcium, you'd have to switch to a pellet made with timothy hay to get less. I think there are some alfalfa pellets with less calcium than Big Red but they still wouldn't be too much different.
You could also try encouraging them to drink more water to help flush excess calcium out. If you feed veggies, rinse them with water before feeding them. You can also give them a second water bowl/bottle and flavor it with a little vanilla, Pedialyte, low-sugar juice, etc. Just make sure that you wash the container out well every day because the sugars can make bad stuff grow.
