My Sta-rite S8M150 System 3 filters look to need replacing. I moved into this house a year ago May. I cleaned the filters yesterday with the pressure at 24 psi before cleaning. After cleaning the pressure only went down to 18 psi. Last time I cleaned them it went down to around 14. They looked pretty rough. I don't know for sure how old they are. I've been in the house over a year. If I had to guess I'd say over 4 years old. Looks like Pool Supply world is the least expensive at around $489 for the large and small set. Anyone else have any suggestions on where else I might want to look? Thanks!