Shell continually getting worse

The pics here are just over 2 weeks apart. He lives in hard water. His food is left over fish flakes/bug bites/brine shrimp, algae wafers and a micro mix for snails and shrimp. I feed some steamed veggies like broccoli, zucchini and kale but I haven’t ever seen him touch it. I’ve been putting cuttle bone in the tank since I’ve noticed the crack forming, but haven’t seen him touch that either. I also add a mineral supplement to the tank that contains calcium for my shrimp. My shrimp are thriving and so are the pest snails. I’ve got some pretty big ramshorn. But I’m at a loss for this guy. Looking for any suggestions on what else to do.