Pool Chemistry

The Science of Balanced Water

For people with water issues, understanding what’s happening and what to do about it can be difficult and treatment expensive.  The key is to stay on top of it by regularly testing and treating the water.  All too often, pool owners think that chlorine, either traditional powder, tablet or liquid treatment or by salt chlorination, is enough to cure all that ails the water.  It’s simply not true.  The water must be in balance or the chlorine that’s added can become ineffective.

Perfect water balance is determined by pH, alkalinity, calcium hardness and Total Dissolved Solids (TDS).  For pool water to be “balanced”, all these factors must stay in their proper range. The ranges may vary slightly, depending on the finish of the pool and the average temperature of pool water during the swimming season.

pH is the most important factor in balancing water. It’s measured on a scale from 0 to 14, with 0 being the most acidic, 7 being neutral and 14 being alkaline. pH must be maintained in a narrow window between 7.2 and 7.8 for a pool to be considered balanced. Pure water is neutral. It’s only when things are dissolved in it that it skews one way or the other.

This is a crucial point – high pH lessen the effectiveness of the chlorine that sanitizes a pool. If your pH is out of whack, it may not matter how much chlorine you dump into the water.  When pH drifts up, water becomes alkaline and creates an environment where mineral deposits (scale) can form and chlorine becomes ineffective at its primary task – killing bacteria and algae. The secret to controlling pH lies in controlling the alkalinity. It acts like a ceiling over your pH, so the pH can only rise so high. It’s important to control the alkalinity first because it makes balancing pH easier. Alkalinity needs to stay within 80 to 120 ppm.

Calcium and total dissolved solids (TDS) such as magnesium, above 300 parts-per-million (ppm), make it hard to get clear water and it compromises the effectiveness of the chemicals. This can be commonplace, depending on your location.

For example, hardness in Phoenix tap water has been seen as high as 1000ppm. Besides tile scale, other severe warning signs of high levels of hardness include scaling on pump, filter and plumbing lines, white deposits in filter sand, white stains on decks and landscape and increasing disinfectant chemical consumption.

Unfortunately, high levels of minerals like calcium and magnesium cannot be cured through normal pool maintenance. These minerals need to be removed. Refilling your pool with the same water you started with is self-defeating, wastes time and water. Some professionals recommend adding a compound that binds to these minerals, but that’s a short-term solution. Cloudy water can reappear. If you’re in a high mineral area, the best way to control an out-of-control calcium or magnesium situation is to have water trucked in.