A certain chemistry: wondering about bad 'chlorine smells' or the ideal pH? This list of 10 common mistakes to avoid will help you answer all your questions.(Chemistry)

Few elements of pool operation are more confusing than chemistry. Even seasoned professionals can sometimes wind up scratching their collective heads about how to solve a particular water-chemistry problem. But there are some common problems that almost anyone can remedy--simply by knowing the right information.

1 Forgetting that high amounts of chlorine can bleach DPD test reagents clear, appearing to show zero residual

More spas are fried and bathing suits bleached because of this error than just about any other. As you know, the universally accepted DPD test for chlorine turns progressively pinker as higher residuals are encountered in the sample ... that is, until the indicator itself is bleached to clear. This phenomenon occurs somewhere near 20 ppm chlorine; the actual value varies with different pH or total alkalinity conditions. Many, many untrained operators or "helpers" have dumped excessive amounts of chlorine in their water (most often in hot whirlpools or spas), thinking all along that for some crazy reason they just hadn't yet put enough in to get a reading! In a small body of water, this testing error has resulted in a few hundred parts per million chlorine residual, creating some very unsafe, damaging or at least unpleasant conditions.

2 Figuring chlorine into pool-water balance

Chlorine has nothing to do with "balance," while pH, temperature, total alkalinity, calcium hardness and, to a much smaller degree, total dissolved solids make up the group of five variables commonly used to calculate the Calcium Saturation Index. This numerical index often is used as the prime indicator of the water's so-called balance. This CSI value helps an operator predict his or her water's aggressiveness, its scaling potential, or the state of balance between those extremes. Chlorine, while critical, is simply the oxidizer/sanitizer compound one adds to the nicely balanced water.

3 Thinking there's too much chlorine in the pool when you can smell it

This familiar cry of the swim-team mom is the most common error of all relating to pool sanitation. The truth is, when you smell it, there's been too little chlorine in the pool--too little for too long. Low chlorine residuals were probably held for a period of days, during which ammonia-type introductions occurred. This urine, sweat and decomposing organic matter produces ammonia compounds of chlorine, commonly called chloramines, which is the source of the odor and irritation.