Water Exchange Calculator
Estimate a partial drain or refill for CYA, calcium hardness, salt, TDS, or metals. The math assumes ideal mixing; real results can vary if the water does not mix evenly.
Before you drain
Treat shell, drain, groundwater, and discharge rules as stop checks before you pump.
- Manuals, local code, and site conditions win over Poolometer.
- High groundwater or saturated soil can float a shell or push pool walls inward when the water level drops.
- Use a qualified pro if the next step could change shell support or drain-cover safety.
- Retest after refill and full mixing before planning another exchange.
Solve for the exchange percent
Start with the reading you have and the target you want.
Target exchange updates automatically
Project a known exchange percent
Start with a planned drain/refill percentage and see the new reading.
Projection updates automatically
Assumptions
- • The replacement water is treated as a single source reading.
- • The calculator assumes the exchanged water mixes fully before you retest.
- • The math is linear for concentration-style readings only.
Important limits
- • Structural, groundwater, and drain risk varies by vessel and site.
- • Hydrostatic pressure can float a shell or bow/cave pool sides inward when the pool is drained too far.
- • Vinyl, fiberglass, and plaster do not share the same empty-shell tolerance.
- • Check local discharge, sewer, and storm-drain rules before pumping water out.
Source-water caveats
- • Metals in fill water can reintroduce the same stain risk you were trying to reduce.
- • High salt, CH, or TDS in the source water can limit how far a refill helps.
- • Staged exchange may not match a one-shot drain if the water mixes unevenly.
Educational guidance only. Verify labels, manuals, local code, and site conditions before acting. Stop for electrical, gas, structural, drain, drowning, injury, emergency, or chemical-mixing risk.