Pool Chemistry Explained
A plain-language reference for every pool chemistry term. What each one means, what range to aim for, and why it matters. No jargon, no fluff.
Sanitizers
Free Chlorine
The active chlorine in your water — what actually sanitizes. Target depends on your CYA level.
Combined Chlorine
Spent chlorine bound to organics — the source of "pool smell," eye irritation, and the signal that your FC is losing the chemistry race.
Total Chlorine
Free chlorine plus combined chlorine. The reading that misleads on its own — only useful when paired with FC.
Chloramines
The compounds responsible for "chlorine smell" and eye irritation — and why the fix is more chlorine, not less.
Breakpoint Chlorination
The shock level that destroys chloramines and resets your chlorine — and the CYA-based target that determines exactly how high FC needs to go.
Oxidation Reduction Potential
A direct measure of sanitizing strength, used widely in EU and pro systems.
Coming soonWater Balance
pH
How acidic or alkaline your water is. The reading that controls chlorine effectiveness — high pH wastes most of the chlorine you add.
Total Alkalinity
The buffer that keeps pH stable. Too low and pH swings wildly; too high and pH drifts upward no matter how much acid you add.
Calcium Hardness
The biggest single lever for LSI. Too low = corrosive water attacking plaster and metal. Too high = scale on tile, heaters, and salt cells.
Langelier Saturation Index
The water balance number that ties pH, TA, CH, and temp together — and why most calculators get it wrong.
Stabilizers
Salt & Other
Salt
The sodium chloride that lets a salt water generator make chlorine — and why salt pools are still chlorine pools.
Total Dissolved Solids
Everything dissolved in your water — minerals, salts, chemicals.
Coming soonPhosphates
Algae food — but not the cause of green pools. What phosphates actually do and when they matter.
Borates
Optional additive that buffers pH and inhibits algae growth.
Coming soon