Pool Water Replacement Calculator
Estimate how much water exchange could reduce a measured pool level of stabilizer, salt or calcium hardness. This calculator includes the level in your refill water and models both a single drain-then-refill exchange and repeated partial exchanges with mixing between cycles.
Estimate dilution needed to lower CYA, salt or calcium hardness, including the level already present in refill water and repeated partial exchanges.
How to use this calculator
Source-water concentration matters. Replacing hard pool water with similarly hard source water may not reach the goal you expect. Entering the refill-water test result shows whether the target is mathematically achievable before planning an exchange.
- Enter pool gallons and current, target and refill-water levels in ppm.
- Choose the percentage replaced in each modeled partial exchange.
- Review the dilution result and ask a pool professional to determine a safe exchange method.
Worked example
For 20,000 gallons with a current level of 100 ppm and a target of 50 ppm, refill water at 0 ppm gives a one-exchange estimate of 50%, or 10,000 gallons. Four separate 20% exchanges, each followed by complete mixing, would reduce the modeled level to about 40.96 ppm.
Example inputs illustrate the calculation. Enter your own measurements, product directions and rates to plan your pool.
Turn your result into a plan
Use the filling-cost calculator to estimate the water charge for a planned exchange. The dilution result does not establish a safe draining depth or procedure. Shell construction, groundwater, equipment and local discharge requirements need assessment before any work.
Frequently asked questions
Can I reach a target below my refill-water level?
Not by diluting with that source. If the source level is at or above the target while the pool needs a reduction, the calculator identifies the target as unachievable through this method.
Why do repeated partial exchanges use more water?
After each refill and mixing cycle, the next removed water includes some of the fresh water added previously. The concentration therefore changes differently from one larger exchange.
Does this model simultaneous draining and refilling?
No. It assumes water is removed, the pool is refilled, and the remaining water mixes before another cycle. Continuous displacement or treatment methods need a different model.
Should I drain the calculated amount myself?
The calculation is a concentration estimate. Have a qualified pool professional determine a safe method and water level; draining can create risks that the dilution formula does not assess.
Continue your pool planning
Need help choosing pool equipment?
Send Pool Supply Depot your pool size, calculator results and existing equipment details. We can help review product options and the information to confirm with your installer. Based in Henderson, Nevada, we serve pool owners and pool professionals nationwide.
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