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Drain / Refill to Lower Salt

Calculate how much water to replace to reach your target salt ppm.

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If you don’t know, use 0–300 ppm as a rough guess, or test your fill water.
Recommended water replacement:
SWG note: Always confirm your salt target in your salt cell manual (different cells like different ppm). After refilling, circulate thoroughly, then retest salt before adding more.
Practical tips:
  • Large drains can risk liner shifting/floating and structural issues.
  • If replacement is large, consider multiple partial drains/refills.
  • After refill: circulate, retest, and adjust slowly.
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Safety note: If you’re unsure about draining, especially with high groundwater, consult a pro.

How the Drain and Refill Calculator Works

This calculator estimates how much pool water must be replaced to lower salt from the current reading to a selected target. It uses the pool volume, current salt level, target salt level, and the salt content of the replacement water.

The fill-water reading matters because replacement water may already contain some salt. The calculator uses that value to estimate the percentage and amount of water that must be exchanged.

Why Salt Gets Too High

Salt remains in the pool when water evaporates. Repeated additions, salt-based chemicals, softened water, and incorrect testing can gradually push the level above the salt cell manufacturer’s recommended range.

Backwashing, splash-out, leaks, and draining lower salt because they remove actual pool water.

When Water Replacement May Be Needed

  • The salt reading is above the salt cell’s operating range.
  • The system shows a high-salt warning or shuts down.
  • Too much salt was added by mistake.
  • The pool also needs to lower CYA, calcium, or other dissolved material.
  • A reliable second test confirms the high reading.

Common Salt-Lowering Mistakes

  • Draining before confirming the reading with another test.
  • Using a generic target instead of the salt cell manual.
  • Ignoring the salt level in the fill water.
  • Adding more salt before the refill water is fully mixed.
  • Draining too much from a vinyl-liner pool.

Frequently Asked Questions

Can salt be lowered without draining?

In most residential pools, salt is lowered by replacing water with lower-salt water. Ordinary pool chemicals do not remove it.

Does evaporation lower salt?

No. Evaporation removes only water. The salt stays behind, so topping off returns the water level but does not reduce the salt concentration.

How accurate are salt-cell readings?

Cell readings can be affected by temperature, scale, age, and calibration. Confirm a high reading with a separate salt test before draining.

When should I retest after refilling?

Run the pump long enough to mix the new water thoroughly, then retest before making any additional salt adjustment.

Pool Gal Pro Tip 💦

Trust, but verify. Before draining thousands of gallons, confirm the salt with a second test and check the exact range printed in the salt cell manual.