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Water Chemistry · B14

Pool TDS Dilution Calculator

How much water to drain and refill to bring high TDS down to your target level.

Measure the inputsThere's no chemical that removes TDS — only diluting with fresher water lowers it.
Read the full resultTest your fill water's TDS first; if it's already high, dilution has limited benefit.
Check the boundarySalt pools naturally run high TDS (the salt counts) — judge them by salt level, not raw TDS.

Useful forWater ChemistryPlanningComparisonVerification

Live calculation

TDS dilution

✓ Checked May 2026

Enter current TDS, target, and your fill water's TDS.

Change a value. See the result.

Required fields are marked *. Engine validation and warnings remain active.

Enter the known values. Let the engine handle the calculation.

✓ Formula checked↻ Live result○ No account needed

Planning estimate only. Confirm product labels, equipment specifications, qualified-professional advice and local requirements before acting.

The result, explained

Use the Pool TDS Dilution Calculator result with context.

How much water to drain and refill to bring high TDS down to your target level.

01

The purpose

What does this calculator estimate?

How much water to drain and refill to bring high TDS down to your target level.

02

The tool

What information does it use?

  • Pool volume: enter a measured or verified value
  • Current TDS: From a TDS meter, in ppm.
  • Target TDS: Under ~2,000 ppm for non-salt pools.
  • Fill water TDS: Test your tap or well water; often 200–400 ppm.
03

The method

How to use this calculator

  1. Pool volumeEnter the value you can verify.
  2. Current TDSFrom a TDS meter, in ppm.
  3. Target TDSUnder ~2,000 ppm for non-salt pools.
  4. Fill water TDSTest your tap or well water; often 200–400 ppm.
04

The relationship

The formula in plain English

Drain fraction = (Current − Target) ÷ (Current − Fill water TDS)

Multiply the fraction by pool volume to get gallons to drain and refill.
05

Worked through

A worked example: 15,000 gal pool, TDS 2,500 → 1,500 ppm, fill water 300 ppm

  1. Drain fraction = (2,500 − 1,500) ÷ (2,500 − 300) = 0.4545
  2. Gallons = 15,000 × 0.4545 = 6,818 gal
  3. Drain and refill ~6,818 gallons
Percent of water to drain to hit 1,500 ppm TDS, with 300 ppm fill water.
Current TDSDrain %Gallons (15,000 gal pool)
2,000 ppm29%4,412 gal
2,500 ppm45%6,818 gal
3,000 ppm56%8,333 gal
3,500 ppm63%9,375 gal
4,000 ppm68%10,135 gal
5,000 ppm74%11,170 gal
06

Why it matters

How the result supports the next decision

There's no chemical that removes TDS — only diluting with fresher water lowers it.

Test your fill water's TDS first; if it's already high, dilution has limited benefit.

07

Good inputs

Improve the estimate before relying on it

  • There's no chemical that removes TDS — only diluting with fresher water lowers it.
  • Test your fill water's TDS first; if it's already high, dilution has limited benefit.
  • Salt pools naturally run high TDS (the salt counts) — judge them by salt level, not raw TDS.
  • Very high TDS can dull water clarity and make chemicals less effective, prompting a partial drain.
  • Drain and refill in stages on a hot day to avoid leaving the shell empty and risking pop-out.
08

The boundary

How to interpret the result

Follow the product label, add chemicals separately and retest before another dose.

The engine reports invalid inputs and safety warnings beside the result. Resolve those messages before using the estimate.

09

Before acting

What should override this estimate?

  • Measured site conditions and current test results
  • Product labels and manufacturer specifications
  • Qualified-professional advice and applicable local codes
10

Common questions

Frequently asked questions

What are total dissolved solids in a pool?

TDS is the combined total of everything dissolved in your water — salts, minerals, chemical byproducts, and more. It climbs over time as you add chemicals and water evaporates leaving solids behind. Very high TDS can reduce water clarity and make sanitizer and balancers work less efficiently.

What TDS level is too high?

For traditional (non-salt) pools, keep TDS under about 2,000 ppm. Above that, water can look dull and chemicals lose efficiency. Saltwater pools legitimately run 3,000+ ppm because the salt itself counts as dissolved solids, so they're judged by salt level instead.

How do I lower TDS in a pool?

The only practical method is to drain part of the water and refill with lower-TDS fresh water. The calculator finds the exact percentage to swap based on your current TDS, target, and fill-water TDS. No chemical can remove dissolved solids.

Does evaporation lower TDS?

No — it does the opposite. When water evaporates, the dissolved solids stay behind and TDS concentration rises. Topping up with fresh water adds back volume but only partly offsets the climb, which is why TDS trends upward over a season.

Should I worry about TDS in a saltwater pool?

Not by the raw number. A salt pool at 3,200 ppm salt will read well over 3,000 ppm TDS, and that's normal. Watch the salt level and overall balance instead; only consider dilution if TDS climbs far above the expected salt contribution.

How do you lower TDS in a pool?

Drain a calculated percentage of the water and refill with fresh, lower-TDS water. There's no chemical alternative.

Is high TDS dangerous to swimmers?

No, high TDS isn't a health hazard. It's a water-quality and efficiency issue that can dull clarity and weaken chemical performance.

What's a normal TDS for a pool?

Under 2,000 ppm for chlorine pools; salt pools run higher because dissolved salt is included in the reading.

Primary sources

Use the result with current guidance.

These official references support safe planning context. Product labels, local requirements and qualified-professional advice take priority over a general calculator estimate.