I have to chuckle after I read some of your posts because I have gone through so many of the same things at exactly the same time frame of tub ownership as you.
I use a zorbo and I went through almost a whole bottle of enzyme in the last 4 months. Most of it being used up in the first 2 months.
After the first 2 months, things settled down quite a bit, and I believe it is from our skin getting cleaner from the hot soaks. Your extra oils come off, your dead skin cells float off, you are sweating while you sit in the tub which further cleans your pores out....
I'd like to think that my whole family is a heck of a lot cleaner than we used to be.
Every so often, I can now feel a dried line--it has no color. If I ever do get back to the days of the dreaded colored tub ring, it is due to the kid's friends (the unclean) that have joined us.
I have about one more use of the enzyme left and then I will change things up a bit for the winter water. I'm going to try N2, my usual dichlor, and shock with MPS. I am also going to try the 4-in-1 SeaKlear once a week to help prevent the dreaded rings!
I think things will settle down for you after 2 months of both scumball and a bottle of enzyme!