I have a 18x36 in ground vinyl pool. Hayward 1.5 HP pump with 300 lb sand filter. 3 ft deep on one end, down to 8 feet on the other. We didn't get to cover our pool this past winter, and, I know better this winter. We have shocked, flocked and thought we were ready to rock, however, the pool just isn't clearing. We feel a rough surface on the pool walls. Last water test were.....

Free Chlorine: 4.13
Total Chlorine: 4.72
pH 7.5
Total Akalinity 75
Calcium Hardness 129
Cyanuric Aciid 53

I haven't changed the sand in the filter for about 3 years. We have brushed the walls, the material feels gritty and hard. Can't see the bottom of the pool. Water really cloudy, (Was REALLY) green. Does anyone have any suggestions?