A few things
1) Those numbers are impossible. You can't have zero alkalinity and a pH of 8.4. Where are you getting those test results from?
2) Your subject line describes the pool store merry-go-round, where you go up and down endlessly but always end up in the same spot.
3) If TC is 10 and FC is 0, then CC is 10, which means your pool would probably smell strongly of chlorine, and burn peoples' eyes. Unless one of the many chemicals you've been dumping in your pool is non-chlorine shock that misreads as CC. But then again, see point 1). I suspect bad testing more than 10 CC
Without accurate consistent test results you're working blind. It will be like trying to paint a picture wearing a blindfold. Sure, some paint will get on the canvas, but you won;t like the final result and a whole lot of paint will be wasted. The canvas will be spoiled, too.
Again, where did those test results come from?