Rolled up dollar bill?

Scrape with credit card first then a razor blade?

We have dark grey tiles on our shower floor and I am re-caulking the gaps between it and the white subway tile wall. I have noticed in the gap and on the floor is a white powdery looking substance that I thought was caulk residue but I think may be lime or calcium deposits. It won't come off. I've tried white vinegar. My DH bought lime away but it says not to use on colored grout or ceramic tile. Suggestions? I want to get rid of it before re-caulking.