Thanks for the info.
I have changed the water - started from scratch. I've had my tub for five months and am on cartridge #4. Changed the water, tested/removed phosphates, ensured pH, alkaline, salt, etc. are at optimal levels. One thing I didn't do was flush the system with Ahh-some, which has seemed to help others.
I'm not completely sold on the idea of turning off/by-passing the salt system; that's why I got it, to enjoy the "feel" of the soft, odorless water with what I thought would be minimal maintenance. But, if I ever do go that route, I appreciate the guidance.
I'm getting my water tested one more time tomorrow...hoping for some sort of obvious diagnosis to end the cartridge frustration.