According to this survey, the salt level of a saltwater pool should range between 2600ppm and 3300ppm. The survey suggests that the frequency is not determined by time, but by PPM levels. Since this particular question seems to have a number of varying answers, talk to your local pool specialist to see what they feel is best for your area.
                
  | Answer: Not sureExplanation: As needed.
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  | Trusted Waters | 
  | Answer: Once a monthExplanation: You may need to add salt every 1–3 months, depending on the above factors. Some pools may require less frequent adjustments.
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  | Cabana Pool Service | 
  | Answer: After it rainsExplanation: You typically need to add salt to your saltwater pool only when the salt level drops, which usually happens due to splash-out, backwashing, or heavy rain. Under normal conditions, salt doesn’t evaporate or break down, so you may only need to add it once or twice a year. It's important to test your salt levels regularly to ensure they stay within the recommended range, usually between 2,700 to 3,400 ppm (parts per million), depending on the manufacturer’s guidelines.
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  | PoolLogic Pool and Spa Service | 
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  | ProMatcher | 
  | Answer: Once at the beginning of each seasonExplanation: At the beginning of the season you should add salt and then on a as needed basis.
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  | Blue Diamond Oasis Pool Cleaning Services | 
  | Answer: Once a monthExplanation: Usually about once a month, sometimes more, sometimes less, but this is the avg.
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  | Larry Braziel Consulting | 
  | Answer: Once a monthExplanation: when the salt level drops below 3300 ppm
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  | Naples Pool Life - POOL CLEANING SERVICE | 
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  | ProMatcher | 
  | Answer: After it rainsExplanation: Only after a rain, or adding fresh water to your pool.
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  | All Weather Pool Service | 
  | Answer: Once a monthExplanation: Depends on salinity and other factors to maintain proper level
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  | Sonny Kuhl's Powerhouse Pool Service | 
  | Answer: NeverExplanation: Never, is a harsh word.
 Since salt does not evaporate, you will rarely need to add more salt unless heavy rains dilute your pool water or significant water is lost from excessive splashing
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  | WaterBender Pools | 
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  | ProMatcher | 
  | Answer: Once a monthExplanation: when it needs it, as different times of the year it will need it more often.
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  | Affordable Pool Pro | 
  | Answer: Not sureExplanation: Once the recommended level has been established, salt level maintenance is minimal. Salt is then added due to loss of salt because of backwashing the filter, bathing suit drag out, water splash out, leaks, or rainwater overflow.
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  | Dream Pools Inc | 
  | Answer: NeverExplanation: Only if needed
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  | SDPOOLMASTER | 
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  | ProMatcher |