Pool Salt Calculator

Why a pool salt calculator is necessary

A saltwater pool uses a chlorine generator. Its salt cell uses dissolved salt to make chlorine.

The salt cell operates at a specified salt concentration. Parts per million, or ppm, is the unit for this concentration.

If the salt concentration is too low, chlorine production can decrease. Too much salt can stop chlorine production in some equipment.

Too much salt can also cause damage to pool equipment or surfaces. Salt concentration alone does not show if the water is safe for swimmers.

Pool salinity calculator: how it works

The calculator uses pool volume, current salt concentration, and target salt concentration. Its gallon unit is US gallons, not imperial gallons.

1. Enter the pool volume.
2. Enter the current salt concentration from an accurate test.
3. Enter the target concentration from the equipment manual.
4. Enter the salt quantity in each bag.

The result shows pounds or kilograms of salt to add. It also shows the number of full bags to buy.

The necessary salt quantity increases with pool volume and the difference between target and current concentration.

Formula

For 100% pure salt, use this approximate formula:

$$\text{Salt (lb)}=\frac{\text{Volume (US gal)}\times\max(0,\text{Target ppm}-\text{Current ppm})\times8.3454}{1{,}000{,}000}$$

For lower purity, divide the result by the purity fraction. For example, 99% purity has a fraction of 0.99.

The calculation treats one liter of pool water as approximately one kilogram. It does not model temperature effects on water density.

The result is zero when the current concentration is equal to or higher than the target. More salt cannot decrease a high concentration.

Pool salt calculator: bags to buy

A 10,000-US-gallon pool has a current concentration of 2,400 ppm. The target is 3,200 ppm.

The difference is 800 ppm. At 100% purity, the estimate is approximately 66.76 pounds of salt.

Two 40-pound bags contain 80 pounds. This exceeds the calculated quantity.

1. Buy two 40-pound bags.
2. Add one full bag.
3. Weigh approximately 26.76 pounds from the second bag.
4. Add that measured quantity.

Do not add all the salt because the bag count rounds up.

Typical salt concentrations for saltwater pools

A range of 2,700-3,400 ppm applies to some chlorine generators, such as the Hayward Salt & Swim 3C. Its example target is 3,200 ppm.

The Hayward manual specifies this range. A different range can be necessary for other equipment.

Use the recommended concentration for your salt cell model. The calculator's initial 3,200 ppm value is an example, not a target for all equipment.

How to add pool salt correctly

Use the equipment manual if its instructions are different from this general procedure. A delay before salt addition can be necessary for new or resurfaced pools.

1. Read the salt-addition instructions for your equipment and pool surface.
2. Set the chlorine generator to the salt-addition mode specified in its manual.
3. Keep the circulation pump on as specified in the manual.
4. Dissolve the salt in a different container only if the manufacturer's instructions specify this method.
5. Apply the measured salt equally across the pool as specified in the manual.
6. Use a brush to remove salt piles on the pool floor.
7. Let the salt dissolve fully.
8. Keep the circulation pump on for the specified period.
9. Do a salt concentration test again.
10. Add more salt only if the new test shows a deficit.

Do not put salt into the skimmer. Salt piles can cause damage to some pool surfaces.

The Pentair IC15 instructions specify that the generator must be off during salt addition. The circulation pump stays on.

Those instructions specify 24 hours of circulation before an independent salt test. Follow your own model's period before you start the generator again.

Pool salt calculator: maintenance tips

Water loss and replacement can change salt concentration. Water evaporation alone does not remove salt.

1. Do a salt concentration test each month, or at the shorter interval specified by the manufacturer.
2. Do the test again after heavy rain, a large water change, or a salt warning.
3. Examine the salt cell for mineral deposits at the interval in its manual.
4. Clean the salt cell only when necessary with the manufacturer's procedure.
5. Do independent tests of chlorine concentration and other water-balance values.

Mineral deposits on the salt cell are called scale. Acid treatment that is not necessary can cause damage to the cell coating.

If the salt concentration is too high, do not add salt. Contact a pool professional for advice before water removal.

Water removal can cause damage to a pool when groundwater pressure is high. This calculator does not give an estimate of that risk.

Related calculators

• Use the cubic feet calculator for a rectangular pool's volume and its conversion to US gallons.
• Use the scientific calculator for an independent calculation with the salt formula.
• Use the sig fig calculator to examine significant figures in measurements.
• Use the percentage decrease calculator to calculate a decrease between two salt-test results.
• Use the time duration calculator to calculate elapsed circulation time from start and end times.

These tools do not replace the equipment manual or a salt test. Significant figures show measurement precision, not water safety.