I'm sure this has been discussed before.......but I have a 5 year old 30' AG pool with a 150 lb sand filter.
The local pool guy says that you should change the sand every 3-5 years.
Another pool guy say you never have to change it, in fact, he says it filters better as the sand gets ground up into smaller pieces.

The first guy says that sand can get clogged with oils and gunk, and will get clumpy and "bad" and less efficient, and that you make your filtering better and more efficient by changing it. He says he has had pools "go bad" and nothing chemically has been wrong, and that the only fix was to change the sand.

My sand does have a thin layer of crusty gunk, but if I take that off, the sand looks brand new. I do not think I need to change it. The first guy says it could be "bad" down on the bottom.

Any thoughts?