Pool is clear but bottom looks spotty and dirty

[rkrgk]

I had Algae issues last season and followed the advice this forum gives and it has been going well. I dont know if I started noticing more this season or that there is something going on with my pool.
First of all, I have to admit that I dont know what material my pool is made of. Usually I use a plastic brush to brush algae off the walls and the bottom, but since I saw lot of algae buildup last two months and they were so stubborn to remove with a normal plastic brush, I bought a wire brush and used a bit on the walls. I was a bit scared to use it liberally since they seem a bit harsh on the surface. But since I really dont know what the surface is made of I am not that confident about using them. I am attaching a picture with this and if someone could identify what type of surface my pool has, it will be really helpful.
There are lot of black dots/patches at the pool side and the bottom and I felt that after I brushed with the wire brush, I see black particles coming off the wall, I thought they were part of the pool surface (assuming the pool is some type of stone type material), it could be algae as well.
So, is it really okay to use the wirebrush on my pool? will it scratch or destroy the surface, is the black spots really because the surface is disintegrating? Or is it black algae?