Concrete pool bottom dirty or cloudy or both?

Forgive me first off. I am a pool newbie in ever facet of the word. I finally have my pool chemically in balance and pretty clear and blue. But when I take a brush to it it generates a huge what looks like a dust cloud. But the floor doesn't really look dirty. I have vacuumed with both types and doesn't seem to clear it. Is this dirt or possible grime from the concrete? The pool is almost 30 yrs old and not sure if its ever been acid washed or replastered

Any ideas?