Excessive MPS shock

[Chillaxin]

New hot tub owner here.  I have been using the Cleanwater Blue system from The Spa Depot.  Everything seemed to be going fine for the first four weeks, but about two weeks ago I started feeling itchy and developed a mild rash on my chest.  The quick start guide that came with the Cleanwater kit said to shock the water with 1 - 2 teaspoons of non-chlorine shock per 100 gal. after each use, which I followed religiously.  Because I was using the hot tub twice a day, I was shocking the water twice a day, seven days a week.  I have subsequently learned that I should only be shocking the water once per week, so I believe the amount and the build up of MPS was probably the cause of my rash.  I stopped using the hot tub five days ago the the rash and itchiness have already disappeared.

I know there is also the possibility the cause of the rash was bacterial, not chemical.  I shocked the water with dichlor five days ago and stopped the MPS shock altogether.  I going to (carefully) start using the hot tub again and see if the rash reappears.  If it does, I will probably do the whole flush, drain, decontaminate and refill routine.

I'm wondering if the MPS level will dissipate over time, or if draining the hot tub is the only way to get rid of it.  I'm planning to shock only once a week if things stabilize and the rash does not return.

Thoughts?