How do I fill wide gap between tub and tile...caulk?
I'm thinking you'd be better off jacking that tub back up and reinforcing it. After you get that gap to less than a half an inch, I'd go with a standard tile wall grout. Do not use a pre mixed grout from a bucket. That is not for wet areas. Get the dry, non-sanded grout in the color of your choice. For filling a gap more than 1/8th of an inch, you should use a thick mixture, and be sure to use a rubber grout applicator, then wipe it with a soft wet sponge, or cheese cloth to smooth and form the joint. I think you'll be happier with this repair than if you caulk it. Caulking tends to mold in bathtubs, and peels away from the tile and/or tub, causing more leaks.