Grout Repair

I have a gap that is going around between the deck and the tile line. It's like the grout is falling apart, that is if it is grout or maybe some other sealant.

I went to Home Depot and picked up a tube of Dap 3.0 Concrete and Masonry caulk that says that it's 100% water proof. Can that be used or is there a specific type of grout for pools that I should use? Or maybe something else?

Thanks,

Actually never mind as I think the post on 6/2 by wsommariva probably answered my question