I take it you didn't fill the tub the first time you caulked. That could be the issue. When you say cracking, do you mean separating from either the tub or the tile or is the caulk actually cracking within itself? If there was dust on either the tile bottom or the tub, you won't get good adhesion. Another possibility is that the caulk doesn't has the flexibility for the job. I always use a 100% silicone caulk in that area and at the wall junctions. Sometimes it doesn't match exactly, but it doesn't separate either.
I'd remove it all and start again. You can use a razor from a utility knife to carefully slice off the old caulk enough to get it ready for the new caulk.
Ron
I'd remove it all and start again. You can use a razor from a utility knife to carefully slice off the old caulk enough to get it ready for the new caulk.
Ron
