I can't tell you if it's OK to use a wire brush - sorry.

It looks to me like the black stuff is something growing that will need to be killed. The fact that you've had algae recently, you have a measurable CC, and you feel you've been using excessive amounts of bleach supports the idea that you're fighting some bio-growth in the pool.

I'd recommend that you shock the pool. Are you familiar with the shock procedure recommended here? If not, a recap:
Raise the FC to shock levels (for your CYA level as per Ben's Best Guess Chart - use the 30-50 row as you're close to 30).
Test and restore FC to shock level as often as you can and don't let it fall below shock level.
Run filter 24/7.
Brush as often as you can (at least daily). The brushing is to expose the black stuff to the chlorine, not necessarily to scrub it all off.
Continue this process until one day after:
The pool is clear.
The pool loses less than 1 ppm FC between sunset and sunrise.
There's nearly no CC (less than 1 drop of R-0871 after adding the R-0003).
If there are no swimmers, maybe try the +shock+ level. I understand that black algae (if that's what this is) can hold strong to the tiny pores in concrete.

One other thought; If you use a 10 ml sample (multiply by 0.5 ppm instead of 0.2 ppm)for the FC and CC tests, your testing reagents will last longer.