Here it is 101 today!

I have been continuously putting bleach and brushing the pool everyday for the past two weeks, maintaining atleast 15ppm of FC, I am starting to up the chlorine to 30 since I think its not that easy to get rid of them. The black spots are almost like plaster. Is there any thing else I can do to make it easier to shake them out and remove them? I am able to get rid of them, but only little by little and not sure if I can remove them completely. Its harder to remove them in the deeper part and under the water fall where it is hard to reach. Can I somehow brush them off with some concentrated chlorine or something?