So I have a sand dollar sd60 sand filter that has started giving me a problem. I will use the vac to clean the pool and the next morning silt / the stuff I just vacuumed out is back in it. Not all of it but a lot of it. The filter is 11 years old and the sand was replaced 7 years ago when we moved but from my understanding it should never need to be replaced. This isn’t filter sand showing up in pool so I assume my laterals are still good. What could be causing this? My spider gasket has never been changed, could that cause it? I am really at a loss. I even added DE to the filter to help out and it may have helped a little but not much. I backwash often and rinse afterwards. Any help would be greatly appreciated.