Why can't I use an OTO test kit when using Sustain? 

OTO does not clearly show the difference between free and combined chlorine and therefore should not be used when the pool is treated with the Sustain Pool Care System. Sustain Summer Shield Chlorine Extender holds a backup reserve of chlorine that tests as combined chlorine. To avoid confusion, use DPD or 3-Way Test Strips to measure FAC without interference.

Note: DPD test kits use phenol red as the pH indicator. Another test that is useful in testing the pH is the Acid Demand Test. Ask your Sustain Authorized Dealer about this test. It shows how much acid is needed to decrease the pH to the target 7.2 - 7.4 range. Remember when using acid to decrease the pH, dilute it in a bucket of pool water and walk it around the pool, adding it in small increments.

Important: Always begin the swim season with fresh test kit reagents: pH indicator, Acid Demand Drops and DPD. Throw away last year's test strips, or if you're using a standard test kit with liquid reagents, replace the reagent dropper bottles and the entire test kit if the color charts have faded.

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