How Often Should I Drain My Swimming Pool? / Do I Need To Drain My Swimming Pool Every Year?

            Yes, your pool should be drained every year. ESPECIALLY IF YOU HAVE A CARTRIDGE FILTER.
       Yes, every manufacturer of every pool made in Arizona says to drain your pool when your hardness is above 750 ppm.
             Yes, every pool every year will hit 750 ppm by the end of that year.
            Fact, in many places in the Valley the water comes out of the tap at over 1000 ppm, and in some places over 1200 ppm.
            Fact, for the last 30 years every manufacturer has said to drain every pool every year. *
* They haven't said it directly, but, because of evaporation, the hardness levels in every outdoor pool double every year. 30 years ago, we had hardness levels around 150 ppm. They all said drain and refill your pool completely at 250 ppm. A few years later it was coming out at 250 ppm. They said drain and refill every pool at 400 ppm. a few years later it was coming out at 350 ppm, they said drain it at 400 ppm. when it came out of the tap at 400 they said 500, 500 they said 650, 650 they said 750. Are you getting the idea? Drain and refill your pool every year.
        Ok, Why? Let's assume that your water is like a freeway, and the chemicals that you add to the water are like emergency equipment. All of the hardness, Total Dissolved Solids, ... and stuff that DOUBLES in quantity in your pool water every year are like traffic on the freeway. algae growth, bacteria growth, ... are all the things that are waiting to happen in every pool. The problem is, the more traffic, the less likely the emergency treatments can get to the areas to treat the problems. So, you either have to increase the number of emergency vehicles already out there (More chemicals) or lessen the traffic. The other thing is that the "traffic" gets stuck on the sides of the road(Tile Line), and at the check points(Filter). This lessens the life span of your filter elements / grids / media, especially in cartridge filters.
            Here's an interesting bit of trivia. Back 30 years ago all of the cartridge filter manufacturers used to print on their boxes and in their instructions, that cartridge filters should not be used in high hardness situations. In parenthesis we had (>350 ppm). At the time, cartridge filters were 1/2 the cost of a sand or D.E. filter. Now cartridge filters are the same as D.E. or Sand, or even higher cost. Now what do we see in the printed material? High hardness can lessen the life span of cartridge filter elements. Interesting. Here's another interesting fact:
            Cartridge filters bring more money into the pool industry annually than all other equipment that you have in the pool. They can easily cost you, the owner, $1000 plus every single year. To keep this in perspective, in most situations, you can buy a high quality sand or D.E. filter EVERY SINGLE YEAR, INCLUDING INSTALLATION, for the cost of the maintenance on your cartridge filter. 
        The number one reason for early cartridge filter element replacement, and more frequent cleans (The two biggest money makers) ... People not doing their annual complete drain and re-fillings of their pool.
                One more thing. not draining your pool every single year costs in other ways as well. Pools that were drained and refilled last year, that are easy to clean, service, and keep nice all year long, will cost me 20% more in chemicals if you do not drain and refill them next year. PLUS, I am going to get about 20% more calls about algae on the walls, tile line, ... cloudy water, ... and 20% more call backs, or extra trips to your house to fix these issues. What does that mean? Well, if you don't drain your pool every year, and you are costing me all of this, plus hurting my reputation, I am going to charge you 25% more for pool service. That's $300 extra EVERY SINGLE YEAR YOU DON'T DRAIN YOUR POOL, AND YOU ARE GOING TO BE LESS HAPPY WITH ME, THE QUALITY OF YOUR WATER, ... EVERY YEAR UNTIL YOU DRAIN AND REFILL YOUR POOL. After 3 years, you will find a new pool man.
            What's the cost of a drain for an average pool, total, with water, labor, ... <$300. (2013 prices)
Your Choice.