I've been wondering the same thing.
I'm a newbie and I thought I finally got a SLAM to work right. I had a couple false starts because I didn't follow ALL the instructions. I didn't get my own complete test kit so I was relying on the pool store to get my CYA number. In two weeks I got four different readings (25, 100, 55, 40) across two different stores. I finally ordered what I needed for my CYA test. I finaly got my chlorine levels right and three days later, no change. I realized I had left the ladders in the pool and I found a ton of algae growing on the bottom of the rungs. Three more days still no change and I was loosing 3-4ppm of chlorine at night. Then I found a skimmer basket full of leaves and two albino dead frogs. I think that was where my chlorine was going.
Finally my water is crystal clear and I'm passing the OCLT test but every morning there is still a very fine layer of what I think is algae on the bottom and some on the angled sides of the deep end. Not too much on the vertical sides.
It seems like the amount goes down every day but it never completely goes away.
How can I verify if it is algae, or dust and pollen?