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Seasoned advice: testing pools with chlorine generators is tricky. Here's what you need to know.

Salt-chlorine generators are becoming more popular among pool owners. A pod equipped with one offers benefits, but does not eliminate the need for routine water analysis, as some of your customers may think. Here's a quick water-testing guide for service technicians who maintain pools that have salt-chlorine generators.

Testing the salt

The salt level doesn't need to be tested often. But you do need to manually check it when the system is installed, and periodically thereafter.

Automatic salt-level indicators, on the other hand, sometimes fail, especially if a cell has scaling. A cell that is not functioning properly may result in a false indication of low salt, so confirm the readout with a manual test before adding more. Stand-alone salt (sodium chloride) tests are sold in drop-count titrations and test strip form.

Testing chlorine

In a traditional pool, free chlorine should be monitored every day to ensure effective sanitizing (target 2-4 ppm). But because the water chemistry tends to be more stable in a pool with a salt-chlorine generator, manufacturers say that free chlorine can be tested less frequently, perhaps weekly.

Easy-to-use, color-matching tests are available, such as DPD reagents used with a color comparator; test strips; or the FAS-DPD titration method, which involves an obvious color change in the water sample and provides more precise results.

As water is recycled through the salt-chlorine generator, there should be little combined chlorine (the irritant that causes the unmistakable odor of a poorly maintained pool). Test for combined chlorine after a pool party, heavy rain or windstorm, or if there are signs of an algae bloom. Choose a DPD test with a color comparator that allows you to determine total and free chlorine. You can then subtract the free reading from the total to get the combined chlorine level.

You can also use the popular FAS-DPD titration, which determines free and combined chlorine without color matching, or a high-end test strip that measures total and free chlorine.

If the combined chlorine level exceeds 0.2 ppm, you will need to superchlorinate the water. Some salt-chlorine generators are equipped with a "boost feature," which enables you to increase the chlorine level over a short period of time (usually within 24 hours).

Or use the traditional method of superchlorination and add more directly to the water yourself. The combined chlorine reading is used to calculate the amount to be added to achieve breakpoint dosage.

After superchlorination, the level should be tested again before the pool is reopened to swimmers. EPA guidelines suggest 4 ppm is a safe re-entry level. Reagents in the DPD chlorine test tend to bleach out at levels around 10 ppm, which makes it difficult to test water that still has a high level of sanitizer.

An alternative is the FAS-DPD method. The reagents used in this method won't be affected by chlorine levels under 20 ppm. Test strips generally offer only 5 or 10 ppm as their maximum.

Testing stabilizer

An outdoor pool being chlorinated with saltwater will require the addition of cyanuric acid stabilizer to slow the rate that sunlight's UV rays destroy the free chlorine residual. Keep in mind, the range recommended by the International Aquatics Foundation is 30-50 ppm.

It's important to test the cyanuric acid level regularly during summer months, when the sun's rays are strongest. Many liquid kits and some multiparameter strips include stabilizer tests.

Testing pH, TA and calcium hardness

Like any pool, those equipped with salt-chlorine generators need to be monitored for the three biggest water balance factors: pH, total alkalinity and calcium hardness.

Manufacturers say that salt-chlorine generators produce chlorine closer to pH neutral--7 on the pH scale--than most other forms (see chart). So this chlorine has less overall effect on pool pH. However, the consequences of improper pH are the same, regardless of the method of sanitation. Thus, you should test the pH weekly in pools with salt-chlorine generators. Easy color-matching tests (with liquid reagents or strips) are available for this purpose. A pH meter also may be used.

The pH is influenced by the TA of the water. When adjusted to within the recommended range, it acts as a buffer for pH. The target for alkalinity is 80-120 ppm. According to manufacturers, there is little fluctuation in the alkalinity due to the chlorine produced from a salt-chlorine generator. However, the generator tends to keep a steadier pH with an alkalinity between 90-100 ppm. Total alkalinity can be checked with a simple drop-count titration. Strips containing a TA test are widely available, but are less useful when adjustments are needed because of their limited range.

When the calcium hardness level is too low, water can become aggressive even if the pH is within the recommended range. It can damage plaster, concrete and grout, and may lead to equipment corrosion. A high calcium hardness level causes the water to deposit scale, also regardless of pH.

This crusty buildup is unsightly and rough to the touch. Deposits can clog filters and piping, as well as cause heaters to fail. Test calcium hardness with a drop-count titration. Test strips will measure total hardness (calcium plus magnesium hardness).

Because the chlorine from a salt-chlorine generator is pure and not combined with additives found in solid products, it does not affect TA or calcium hardness directly. But rain and windborne contaminants, splash-out, carryout and treatment chemicals affect these levels. Therefore, to prevent balance-related problems, it's recommended that alkalinity is checked weekly at the same time as pH, and that hardness be tested at least monthly.

The author wishes to thank AutoPilot, Jandy and Zodiac for their assistance with this article.

Ivusich is sales manager at Taylor Technologies Inc., a manufacturer of recreational water test kits in Sparks, Md.
Chlorine                                    pH
Product                          (in 1 percent

Chlorine gas                                 0
Trichlor                               2.8-3.5
Dichlor                                    6.7
Chlorine from salt chlorinator           7-7.8
Calcium hypochlorite                  8.5-11.8
Lithium hypochlorite                      10.8
Sodium hypochlorite                         13
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Author:Ivusich, Wayne
Publication:Pool & Spa News
Date:Feb 13, 2006
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