Hi! This is my first post! We have a Pentair Quad DE filter that's about 10 years old. We've lived here for 2 years, and the longest we've ever been able to go without a full cartridge cleaning is about 3 months, and that was right after we replaced the cartridges about 6 months ago. There is NO BACKWASH on our system, and we occasionally hose the cartridges down inside the filter but end up having to completely clean them a couple days later anyway. We have no algae growth and our pool chemistry is almost always right on with chlorine, total alkalinity, and pH. We drained it last year also. Pool is 25,000 gallons. We can't figure this out! Help!