Welcome to our forum.
There used to be a person here, Chas, who was a Hotsprings dealer (maybe he's still here) that had a rule of change the water after the first month of ownership - so true!
Everything you are doing is overkill, it's a perfect sign that the bacteria has won the battle. Trust me, I know what your going through, it's a pain in the a-- and it's not going to get any better, if It does, within 24 hrs you'll be back to nasty water. You will be upset with yourself when you see how much effort you are putting into this . When after you purge drain and refill, you will see how easy water care will be.The question is, do you really want to bath in this stuff? Health comes first , trust me not worth it!!!