Read the section under Equipment Cartridge filters. Bottom line ... you are almost paying for a brand new D.E. filter every single year, and those are the best unless you are doing your own maintenance and are lousy at it, or you are going to make the home a rental... 

In general, after you replace your cartridge elements, write down your starting pressure, when the pressure rises 5 lbs. above that, pull apart your cartridge filter and thoroughly clean it, or every 3 months max. (Note: if you have a floor head system this won't work. Clean after every big storm and every 3 months instead.)

When the freshly cleaned pressure of your cartridge elements is above the 5 lb. pressure increase you wrote on the side of your filter, replace your elements. If you are in the Phoenix area pretty much all elements need replacing within 2 years. Understand that as pressures increase water bypasses the elements without cleaning, chemical costs rise, algae and water cloudiness increases ... And your pool man is going to look worse and worse because you aren't allowing him to maintain your pool properly. 

Oh yes. IT IS A REQUIREMENT TO DRAIN AND REFILL YOUR POOL EVERY SINGLE YEAR! Ask any pool manufacturer or reputable company at what hardness level your pool should be drained. Since you never take any water out, in Phoenix your hardness will go up every year by whatever your tap hardness level is. If it's 700 ppm, after a year it's 1400, 2 years 2100 ... And all reputable companies say your pool should be drained at 1000 ppm or even less.