Thank you everyone for your responses.
Calvin sure seems to like the mineral block and the cuttlebone. I was just worried about him ingesting something that could cause a blockage, like 'halfnelson' had stated.

I also remove the hard back off of mine. or I get the turtle cuttle bones it is already removed form those.

Where do you find these?

where do you get the cuttlebone? Is this the same thing as the turtle bone I have seen at the pet store?

yes. same problem here. i also put cuttle bone in their cage. but i don't seem to see changes with the bone. as if they don't even eat it. but i like it when they're playing with it. they're standing on it. and since they're much smaller, it seems like they're surfing with the bone as the surf board. hahaha....