Salt chlorine generators are popular among pool owners because of the convenience of not having to transport, store, and handle chlorine. The promise of less maintenance and lower costs over time also makes this method attractive. But lower maintenance does not mean no maintenance and with any pool or spa, the key to knowing what maintenance is needed lies in regular water testing.
How Salt Chlorinators Work
When a salt chlorinator system is installed, the chlorination process begins with adding pool salt (food grade but non-iodized) to pool water at the correct concentration specified by the manufacturer to produce sufficient chlorine for killing germs. Chlorine is produced as the salted pool water moves through an electrolytic cell, which emits an electric charge that frees chlorine from the salt molecules.
Like other sanitizer products added to water, the chlorine made through the electrolysis of salt water forms hypochlorous acid (HOCl). HOCl kills bacteria and other microorganisms and oxidizes organic contaminants; then it reverts back to salt (chloride) and feeds back through the cell to begin the cycle again.
Keeping your salt level in the optimum range is the key to keeping your pool water properly balanced. Regular water testing of chlorine, pH, calcium and total alkalinity—and treating the water to adjust as necessary—is just as important with a saltwater pool as it is with a pool sanitized by traditional chlorine. Here are some tips to help you keep water quality high while keeping maintenance low in your saltwater pool.
Testing Salt
The salt level does not need to be tested often, but you will need to manually check it when the system is first installed and periodically thereafter. Though some small amounts of salt can be lost in the process due to splash-out and other means, this type of sanitization is essentially self-perpetuating. Your salt chlorinator system should alert you if your salt level is low. However, automatic salt-level indicators can sometimes malfunction, especially if a cell has some scaling. If you ever suspect that a salt cell might be giving a false indication of low salt, you can easily confirm the level with a simple test before adding more. Stand-alone salt (sodium chloride) tests are sold as drop-count titrations or as test strips.
Testing Chlorine
As water is cycled through the salt chlorine generator, any combined chlorine—the irritant that causes red eyes and the unmistakable "chlorine odor" of a poorly maintained pool—is eliminated as it passes over the electrolytic cell. Under normal conditions, there should be little combined chlorine in pools with salt chlorinator systems.
But after a pool party, heavy rain or windstorms, or if there are signs of an algae bloom, you need to test for combined chlorine. We recommend the popular FAS-DPD titration test that determines both free and combined chlorine directly without color matching, or a high-end test strip that measures both total and free chlorine. Colorimeters also may be used for this testing.
If the combined chlorine level is found to exceed 0.2 ppm, you will need to breakpoint chlorinate (shock) the water. Some salt chlorine generators are equipped with a "boost feature" that enables you to increase the chlorine level over a short period of time. Or you can use the traditional method of adding a shock product to the water. The combined chlorine reading is used to calculate the amount of chlorine to be added to achieve breakpoint dosage. After shocking, the chlorine level should be tested again before the pool is reopened to swimmers.
Testing Chlorine Stabilizer
An outdoor pool being chlorinated with salt water will require the addition of cyanuric acid "stabilizer" (CYA) to slow the rate UV rays destroy the free chlorine residual. (The industry-recommended ideal range is 30–50 ppm). It is particularly important to test the CYA level regularly during the summer months when the sun's rays are strongest. Many liquid test kits and some multiparameter test strips include a stabilizer test. Colorimeter tests are also available for CYA.
Testing Water Balance – pH, Total Alkalinity, and Calcium Hardness
These three water balance factors should be checked regularly in all pools, including those with salt chlorine generators. When pH is too high, chlorine's sanitizing ability is lessened and scale tends to form. When pH is too low, the water tends to be corrosive. A pH outside of the acceptable range (7.2–7.8, ideally 7.4–7.6) is also potentially irritating to bathers.
Manufacturers of salt chlorinators say the systems produce chlorine that is closer to pH neutral than most other forms (7 on the pH scale of 0 to 14). This means chlorine produced from salt should have less overall effect on pH. However, a byproduct of the salt-to-chlorine reaction is sodium hydroxide (NaOH). The production of NaOH can push the pH higher, requiring more frequent addition of acid in salt pools. The consequences of improper pH are the same regardless of sanitization method. In pools with salt chlorine generators, daily testing of pH is recommended. Easy color-matching tests (with liquid reagents or strips) are available and a pH meter or colorimeter may be used.
Total alkalinity influences the pH and when kept within the recommended range, acts as a buffer for pH. The target for alkalinity is 80–120 ppm. According to manufacturers, there is typically little fluctuation in the alkalinity with chlorine produced from a salt chlorinator, but the units tend to keep pH steadier when alkalinity is between 90–100 ppm. Checking total alkalinity weekly is recommended with a simple drop-count titration or test strips containing a total alkalinity test. However, strips have a limited range so they are not as useful when adjustments are required. Colorimeter tests are also available for total alkalinity.
When the calcium hardness level is too low, water can become aggressive even if the pH is within the recommended range. It can damage gunite and grout and lead to equipment corrosion. And regardless of pH, a high calcium hardness level causes the water to deposit scale. This crusty buildup is unsightly and rough to the touch. Deposits can clog filters and piping and cause heaters to fail. Calcium hardness is tested with a drop-count titration. Test strips will measure total hardness (calcium plus magnesium hardness), and colorimeters may be used for the calcium test. It is recommended to test hardness at least monthly in pools with salt chlorinator systems.
Because the chlorine from a salt chlorine generator is pure and is not combined with additives found in solid products, this form of chlorination does not affect total alkalinity or calcium hardness directly. However, rain and windborne contaminants, splash-out, and treatment chemicals all affect these levels. Therefore, we recommend using these guidelines to prevent balance-related problems.
The Bottom Line on Water Testing for Salt Pools
Salt chlorinators offer many benefits, but they don’t eliminate the need for routine water analysis. Balanced water and correct salt and stabilizer levels will extend the life of the chlorinator along with other equipment and the pool itself. It will also provide the best possible swimming experience. Test regularly and always follow recommendations of the salt chlorinator system manufacturer.