Why Do We Need to Drain Pools?
Dissolved minerals and solids in your pool (TDS, Calcium, Salts, CYA, etc.) never leave the pool. When water evaporates, it leaves as pure water, and all the dissolved byproducts stay behind. Adding fill water and chemicals to the pool adds to the concentration in the pool water. Over time, those levels become too much for the service technician to maintain proper chemistry levels. Eventually, either the pool will get out of control or you have to add way more chemicals than normal just to keep up. The traditional way of dealing with this has been to drain and refill your pool every 3-5 years; sooner if your fill water is really hard or if you have well water. Commercial pools are recommended to be drained every year.
Total Dissolved Solids
Total Dissolved Solids (TDS) are a total of all the minerals and solids in your pool. The majority of the number is the total of Salts and Calcium in the water. Anything you add to the water, even each time you swim in the water, increases the TDS.
Calcium is one way your pool “buffers” the saturation in the water. Pools want to balance out to 200-400 ppm. When water evaporates from your pool, its leaves behind all the dissolved minerals and goes into the air as pure water. Adding more fill water adds to the concentration of calcium.
Salts are found in all natural water. They rise each time we add chlorine or tap water. Even if you don’t have a “salt” pool the levels will continue to increase. Commercial pools rise at a faster rate as they use more chemicals to balance out the swim load.
Cyanuric Acid (CYA) is needed to protect chlorine from the sun. Not enough and the sun depletes the chlorine in a day. Too much and the chlorine becomes “locked” and ineffective.