I have same problem, but think it's from the street that runs parallel to my pool. It's about 15' from pool and separated by an 8' wooden fence. Problem is that it's a low spot where creek run goes behind my property and then under streets. Two streets actually, since it's a divided street and speed limit is 30. I think this because it collects on the coping--above ground pool.
Anyway, I'll try the DE thing, just to get better filtration. Also wondering how poolboy was doing w/ his problem.