Does Anyone Know How To Better Clean A Pool?

I have a pool that we let friends of our borrow and I ended up getting it back this past weekend. Well I don’t know if they ever cleaned it, but before I set it up in my yard, I cleaned it the best I could and now there are the tiniest little dirt specs all over in it. I’ve tried shocking it, using a net and even a pool vacuum, but the specks are way too small. Even the filter isn’t picking them up. Help please!