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What to Know About Salt Water Pools / Chlorination

Confused on what to know about salt water pools? Our experts have you covered, detailing the important unique qualities that salt water pools offer. Today, chlorine generators in the swimming pool industry use an in-line system. This is a device that contains many cells with pool water passing through it.

Massachusetts Swimming PoolsSalt (sodium chloride) is added to the pool water to a level of 2500 to 3500 ppm. This is dependent on the manufacture and system. Low voltage DC electricity is applied to the inline cell. Then, the unit produces chlorine gas, hydrogen gas, sodium ions, hydroxide ions. However, there is no membrane or separator and the direct mixing of these products result in the formation of sodium hypochlorite instead of the evolution of elemental chlorine gas.

The sodium hypochlorite quickly makes hypochlorous acid (HOCl – the quick kill form of chlorine) and hypochlorite ion (OCl-). The hydrogen gas releases into the atmosphere as it bubbles up into the pool water. Very little of the hydrogen is in the ionic form in the water.

Overall, there are normally two ways a salt generator works:

  1. Varying the amperage to the cell. Since cell life is generally on the basis of how long the cell is in operation and not how much chlorine is produced, this is not usually the best method.
  2. Keeping the amperage on its highest setting and vary the length of time it is on via a timer. The timer can be internal, external, or both.
For example in a pool of 30,000 gallons, the filter may be running 24/7. The salt water chlorine generator is on a separate timer which dials only to operate a percentage of that time. The internal timer on the unit is adjustable to fine tune the production of chlorine. Based upon calculations of one pound of chlorine per 10,000 gallons = 12 ppm; the unit being on 12 hours per day, the setting on the unit would need only be dial able in at about 40% production to achieve 1 ppm.

The Process of Electrolysis

 

Reaction that takes place in an inline Salt Cell:

  1. Sodium Chloride (Salt) added to pool water. Massachusetts Swimming Pools
  2. Anode of cell makes Hypochlorous Acid and Hydrochloric Acid.
  3. Cathode of Cell makes Sodium Hydroxide and Hydrogen Gas.
    (The Hydrogen gas bubbles through the Pool water into the atmosphere).
  4. Hypochlorous Acid from the Anode combines with the Sodium Hydroxide from the Cathode to make Sodium Hypochlorite or Liquid Chlorine when immediately mixed with the Pool water going through the Cell.
  5. Hydrochloric Acid from the Anode combines with the Sodium Hydroxide from the Cathode to make Sodium Chloride (Salt) which is re-usable by the Aqua-RiteCell.
  6. Liquid Chlorine at a pH of 7.4 goes half to Hypochlorous Acid and half to Sodium Hydroxide.
  7. Hypochlorous Acid combines with soil, bacteria, algae, organics and UV’s to convert to Hydrochloric Acid.
  8. Lastly, Hydrochloric Acid combines with Sodium Hydroxide forming Sodium Chloride (Salt) again, which is once again re-used by the Cell.

Thus, this is called a Closed Loop System because the salt is used over and over again. The only loss is through splash out, carry out, back-washing, and rainfall.

The type of salt to use is:

  • Granulated
  • Evaporated
  • Non-Iodized

Be careful, many salt products contain tricalcium phosphate to prevent caking. It’s insoluble and ends up on the bottom or in the filter. Notably, watch out for iodine, and do not use pelletized rock salt or water conditioner salt.

Note: A salt water chlorine generator should NEVER be on when there is no flow / pump is off.

 

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