I have been running it 24/7 for the past week along with a Dolphin (not 24/7 but fairly often) and there is definite improvement. It went from deep green to blue, albeit cloudy blue. After testing the water repeatedly, every number was ok except CYA which is very low. According to the pool guy the filter is running extremely slowly which is why he is hot to replace it. He says it may work (at clearing the water) eventually but could take a few weeks. Just to be clear, it isn't the pool store that wants my filter replaced.

The pressure on the filter is normal (about 20lbs) if that makes a difference and the filter worked fine last season. Could there be a filter problem independent of the sand condition, or is that unlikely?

Thanks for the great responses.