Good point Dave.
Perhaps I am wrong, but I have always had the belief that sand can be worn down, the edges become smoother, due to a high amount of backwashing and constant water movement. If true, this would make it more difficult to remove dirt, organic matter, and dead algae as effectively as it once did.
Until yesterday, I haven't followed the posts on clearing up cloudy or green pools (because I have mainly focused on other issues) and I apologize if I am going against TFP policy. But from my perspective of maintaining pools for my customers, if I have maintained a chlorine residual around 10 ppm for a week, and the cloudy water doesn't clear up, I hesitate about adding a very high dose of chlorine. I have often found that by simply adding DE, filter aids, or clarifiers to pools, (and it always seems like the cloudy water problem has been with sand filters, or older cartridges filters), usually works. Of course, I also put my hand in the filter to stir around the sand as best as I can and try to determine the condition of the sand. If it doesn't clear up, then I have super chlorinated to about 30-40 ppm, and yes, then that usually works in those cases.
Ocassionally, when the pool water just won't clear up, I have brought out a portable DE filter, and within 24 hours, the pool water is clear. Of course, maybe if I had raised the chlorine level to over 50 ppm, then perhaps that would have worked also.
