Credit: USFilter

Common problems with pool-water chemistry can easily be corrected through careful monitoring, testing, and managing.

Credit: USFilter

The only reliable free-chlorine testing method is a diethyl-p-phenylene diamine kit.

Pool problems result from many factors, including chemistry variables, equipment malfunctions, or other upsets. Most common problems with pool water chemistry can be attributed to five factors: free available chlorine residual, total chlorine residual, pH, total alkalinity, or calcium hardness. Fortunately, each factor can be corrected easily through careful monitoring, testing, and managing.

Free available chlorine is the most important, as it can disinfect and oxidize pathogens in the water. Total chlorine residual and pH are notorious for being misunderstood and mismanaged. Although they require less frequent checking and adjusting, total alkalinity and calcium hardness can lead to problems with pH control and pool finishes.

These five factors cause about 90% of all pool water problems, including eye burn, odor, cloudiness, scale, corrosion, short filter cycles, filter calcification, green algae, water discoloration, pool surface problems, and proliferation of bacteria and viruses. Although some of these effects also may result from equipment malfunctions or other upsets, quick and inexpensive tests can determine which, if any, of the five critical factors might be to blame.


Free chlorine is the most important factor in public pool water management. The only reliable method for testing free chlorine is a diethyl-p-phenylene diamine test kit. Flash readings or refrigerated samples with the orthotolidine test reagent are unreliable.

Maximum free chlorine levels vary. Local public health regulations sometimes dictate an upper limit for free available chlorine residual. Other pools set this limit as the point at which people begin to complain about bleached bathing suits, dry skin, and eye burn.

Ultimately, the ideal target at which to set free available chlorine levels differs per pool. No sound evidence exists that pools maintained at one target residual will be better, safer, or more comfortable for users over the long run compared to pools maintained at another residual. However, a higher target residual should be chosen when a greater margin for error is needed. On the other hand, if a lesser margin for error is needed because of automatic controls or specific expert care, a lower target residual is possible.


Total chlorine residual indicates how much chloramine residual is present, compared to free chlorine. This value should never exceed the free available chlorine residual by more than 0.5 parts per million (ppm). Superchlorination ensures that chloramine levels remain at or below 0.5 ppm.

Although a pool's pH rarely is harmful to swimmers, it can affect metal, grout, and plaster on pool surfaces and in mechanical equipment. In addition, pH frequently can alter the performance of other chemicals added to a pool, most of which work best at a pH of about 7.5.

While there are many different pH targets, experts generally agree on a pH that ranges from 7.4 to 7.6. Maintaining such a pH in hypochlorinated indoor pools is not difficult, where operators can effectively counteract gradual shifts in pH. Automatic controls used on many pools also can maintain pH within this range, assuming the chemical feed pump is properly sized and working well, and a proper chemical supply is available. It is usually far more challenging to maintain such tight pH control in gas-chlorinated, outdoor pools without automation.

In terms of long-term costs associated with public pools, controlling pH is the most important factor. It often explains why one pool's mechanical system or plaster finish lasts 35 years while another's lasts only three.