Why won't my pool get clean?

[chem geek]

If it were algae, then it would have some semi-transparent parts to it, especially near the edges. If it were dirt or pollen, then it will look pretty solid. It does sound like you've got some sort of reddish dirt in the pool. In addition to the excellent tests that matt gave, you could also just have a bucket of fresh water near the edge of the pool that gets a lot of this stuff and just see if the bucket of water gets it too. I'm betting that it's blown in dirt at this point. You didn't report any unusual chlorine demand.

Since you were able to scrape up some of this stuff, why not put it into a small container and add some concentrated chlorine to it as matt suggested. If it's algae, it will definitely discolor and turn more gray. If it's dirt, it may not change (you can take some dirt from nearby the pool to see how known dirt reacts to concentrated chlorine).

Richard