Sheepshead minnow male is fully eating rocks

I thought I did a pretty good job at imitating their native habitat, they even have mud/rocks that are a similar make up to the area so I'm worried why my one male is fully eating the substrate. I know they are sifters, but he is swallowing it, I can see it in his belly. They have been eating normally otherwise and his behavior hasn't changed beyond that and sort of just sitting on the bottom of the tank (from the extra weight??). They are comfortable at the bottom but it's my first time seeing him actually just sit there. There are about 6 others with him I belive all female but a few are still too young to tell. Any ideas?