Water chemistry

Salt Pool Service Chemistry and Weekly Routine

Salt, CYA and FC targets for salt chlorine pools, a salt-add worked example and a weekly stop routine for owner-operators.

A salt pool still runs on chlorine. The cell makes it from dissolved salt. Your job at the stop is to keep salt, CYA and pH where the cell can do its work, and to catch scale before it costs a cell.

Targets for a salt pool

At CYA 60 to 80, the 7.5% rule lands at 4.5 to 6 ppm, which is above the general 1 to 4 ppm residential range. The CYA rule governs.

Why salt pools need CYA

A cell makes unstabilized chlorine. Without CYA, sunlight burns it off fast and the cell cannot keep up. With CYA in range, FC lasts longer. The tradeoff is that high CYA needs a higher FC minimum, so check both numbers at every stop. If CYA climbs past what you need, see high CYA and what to do.

Adding salt

Salt is simple math. 1 ppm in 10,000 gallons is about 0.083 lb, so 100 ppm takes about 8.3 lb per 10,000 gallons.

Example: an 18,000 gallon pool reads 2600 ppm and the cell maker's range is 2700 to 3400. You aim for 3200 ppm.

1. Raise needed: 3200 - 2600 = 600 ppm.
2. Multiplier: 18,000 / 10,000 = 1.8.
3. Salt: 8.3 lb x 6 x 1.8 = about 90 lb.

Steps:

1. Follow the cell maker's instructions. Many say to turn the cell off until the salt dissolves.
2. Run the pump. Spread the salt across the shallow end or around the perimeter and brush it to dissolve.
3. Let the pump run for a day, then retest with a reliable salt test.
4. Do not trust a single reading from the cell display. Displays and kits can disagree. Confirm before you add more.

If the reading is above the maker's range, only dilution lowers it. Replace fraction = 1 - (target / current). Example: 4200 ppm down to 3200 ppm is 1 - (3200 / 4200), about 24% of the water. Retest TA, CH and CYA after the refill, since they drop too.

pH drift

Salt pools tend to rise in pH over time, and many owners see it as a weekly chore. Acid is the usual fix.

Example: the 18,000 gallon pool reads pH 7.9. You want 7.6.

• 12 to 16 fl oz of 31.45% muriatic acid per 10,000 gallons lowers pH about 0.2 from around 7.8.
• Multiply by 1.8: about 22 to 29 fl oz per 0.2.
• That is a 0.3 drop. Dose one 0.2 step, retest, then decide whether a small second dose is needed.

The muriatic acid dose chart has the full table. If TA is high, dose TA first.

Scale on the cell

A cell collects calcium scale when pH, calcium or temperature run high. Look at the plates at least every few visits, and clean them per the maker's instructions. The steps are in salt cell cleaning. Heavy scale shortens cell life and reduces chlorine output. If scale returns fast, check pH, CH and the saturation index.

Weekly stop routine

1. Read the cell display, and note output percent and any warning.
2. Test FC, CYA, pH and TA. Test CH and salt on a schedule you set for the account.
3. Look at the cell through the sight glass or union, and clean it when you see scale.
4. Check flow. Low flow trips the cell on many models.
5. Adjust output. Raise it in summer or heavy use, and lower it when FC runs high.
6. Add liquid chlorine to cover a gap. Use the chlorine dose tool for the amount.
7. Log the readings, and note anything that changed.

Cold water and heavy use

Cells make less chlorine in cold water, and many shut off below a minimum temperature the maker sets. Check the manual for the model on your stop. During cold periods or after a party, use liquid chlorine to hold FC rather than running the cell at 100 percent and hoping.

Hard surfaces and fixtures

Salt can affect some natural stone and some metals. Before converting a pool to salt or adding a lot of salt, ask about coping, decks and fixtures. If the customer wants an answer on warranty or damage, send them to the manufacturer or a licensed professional.

Mistakes

• Running the cell at 100 percent to make up for low CYA.
• Adding salt in one big dump without the pump running.
• Trusting the cell display over a test.
• Ignoring scale on the plates until output falls.
• Skipping the CYA check, then finding FC runs low even with the cell working.
• Forgetting to retest salt after a partial drain.

Safety

Follow the product label and SDS. Never mix chemicals. Add chemical to water, never water to chemical. Turn the cell off per the maker's steps before you open it.