Let me share what I did this past weekend.
My pool water was cloudy and I could see small bitts of matter (dead algae) suspended in there. The filter was not filtering well, I thought. I had backwashed it numerous times and nothing, still cloudy water. I have decided to pop the cap where the pressure gauge was and peek inside. The sand did not look that dirty. I have heard about water house and spraying inside method but decided to go one step further. I put the filter on backwash, moved the water supply pipe inside the filter to the side and turned the pump. Stuck my arm inside and started moving sand around. Yeah, water came over the top but you should have seen it. I could not believe how dirty it was. The pressurized water from underneath made sand really "liquid". I kept moving sand around until water that was overflowing was clean then I put everything together and put the filter on rinse and rinsed for about a minute.
The filter has been running overnight and I already see the bottom. Major improvement.
This will be my to do item at the beginning of swimming seasons.