Pool chemistry intimidates a lot of pool owners — there are multiple parameters to track, the interactions between them are non-obvious, and getting it wrong has visible consequences. But the underlying logic is straightforward once you understand what each parameter does and how they relate to each other. This guide covers everything you need to manage pool chemistry effectively, from the basics to the nuances that matter specifically in Florida.
Why water chemistry matters
Pool water chemistry serves three purposes: sanitation (killing pathogens and keeping the water safe to swim in), water balance (keeping the water from damaging your pool surface or equipment), and clarity (maintaining water that's visibly clear rather than cloudy or colored). Getting chemistry right accomplishes all three simultaneously. Getting it wrong compromises all three — and the problems compound.
The five parameters
1. Free chlorine (FC) — target: 1–3 ppm; minimum 1 ppm
Free chlorine is your active sanitizer — the chlorine in the water that's available to kill bacteria, viruses, and algae. It's the most important number to get right on a day-to-day basis. Below 1 ppm, your pool is inadequately sanitized. Above 10 ppm, the water becomes irritating for swimmers.
Free chlorine is distinct from total chlorine (which includes both free chlorine and "used up" combined chlorine, called chloramines). When total chlorine significantly exceeds free chlorine, you have a chloramine problem — commonly responsible for the strong "pool smell" and eye irritation people associate with too much chlorine, when it's actually the opposite.
What consumes it: UV degrades chlorine rapidly (especially without cyanuric acid stabilizer), bather load introduces organic compounds that react with chlorine, and organic debris in the water creates chlorine demand. In Florida summer, chlorine demand is highest due to UV intensity and warm water temperatures.
2. pH — target: 7.4–7.6
pH measures how acidic or basic your water is on a scale of 0–14, with 7 being neutral. Pool water is kept slightly alkaline. pH is the most important factor controlling chlorine's effectiveness as a sanitizer: at pH 7.0, chlorine is approximately 75% effective. At pH 7.8, effectiveness drops to around 30%. At pH 8.0, chlorine is less than 20% effective. This is why a pool can test positive for chlorine but still have algae — if pH is too high, the chlorine present isn't actually doing its job.
What raises it: Carbon dioxide off-gassing (aeration from jets, waterfalls), saltwater chlorination, adding alkalinity increasers. pH drifts upward naturally in most pools.
What lowers it: Rainfall (which is naturally acidic), adding acid (muriatic or dry acid), heavy bather load, adding chlorine products.
To raise pH: Sodium carbonate (soda ash).
To lower pH: Muriatic acid or sodium bisulfate (dry acid).
3. Total alkalinity (TA) — target: 80–120 ppm
Total alkalinity is the water's capacity to resist changes in pH — it's the chemical buffer that keeps pH stable. Without adequate alkalinity, pH swings dramatically in response to any addition (chemicals, rain, swimmer activity). With too much alkalinity, pH becomes resistant to correction and tends to drift high.
The relationship between alkalinity and pH is the most important connection in pool chemistry: alkalinity must be adjusted before pH adjustments will hold. If you lower pH and it bounces back within a day, high alkalinity is usually why.
To raise alkalinity: Sodium bicarbonate (baking soda).
To lower alkalinity: Muriatic acid added in larger doses with the pump off, followed by aeration to allow CO₂ to off-gas and stabilize pH.
4. Cyanuric acid (CYA / stabilizer) — target: 30–50 ppm; maximum 80 ppm
Cyanuric acid protects chlorine from UV degradation. In direct Florida sunlight, an unstabilized pool can lose 75–90% of its free chlorine within a few hours. CYA binds loosely to chlorine molecules and shields them from UV, extending chlorine's life in the water significantly. Without stabilizer, maintaining adequate chlorine in an outdoor Florida pool is nearly impossible without constant re-dosing.
The critical caveat: too much CYA causes "chlorine lock" — a condition where the CYA binds the chlorine so tightly that it becomes ineffective as a sanitizer even though it still tests as present. This is one of the most commonly misdiagnosed problems in pool care. Pools maintained exclusively with stabilized chlorine tablets (trichlor) accumulate CYA steadily over time because trichlor contains CYA as part of its formulation.
When CYA exceeds 80 ppm, the pool needs a partial drain and refill to dilute it back into range. There is no chemical that removes CYA from pool water — dilution is the only solution.
CYA and effective chlorine: As CYA increases, more free chlorine is needed to maintain effective sanitation. At 50 ppm CYA, a minimum of 2 ppm free chlorine is recommended. At 80 ppm CYA, the minimum effective free chlorine level is approximately 3 ppm. Factor this into your chlorine targets as CYA builds up through the season.
5. Calcium hardness (CH) — target: 200–400 ppm
Calcium hardness measures the concentration of calcium dissolved in the water. This matters for surface protection: water that's too soft (low calcium) will aggressively dissolve calcium from your pool surfaces — plaster, pebble, grout — causing etching, roughness, and surface damage over time. Water that's too hard (high calcium) precipitates calcium carbonate onto surfaces and equipment as scale.
To raise calcium hardness: Calcium chloride.
To lower calcium hardness: Partial drain and refill with fresh water. There's no chemical that safely reduces calcium hardness in pool water.
The Langelier Saturation Index
The Langelier Saturation Index (LSI) is a formula that combines pH, alkalinity, calcium hardness, temperature, and total dissolved solids into a single number indicating whether your water is balanced, corrosive, or scale-forming. A professional service company should be calculating LSI as part of their chemistry management — it's the most complete picture of your water's overall balance. An LSI between -0.3 and +0.3 is the target range.
The order of operations
When multiple parameters need adjustment, follow this sequence:
- Adjust alkalinity first — it's the foundation that controls how everything else behaves
- Adjust pH — once alkalinity is correct, pH adjustments will hold
- Adjust calcium hardness — less urgent than pH and alkalinity, but should be in range before shocking
- Adjust cyanuric acid if needed — add stabilizer if low; drain and refill if too high
- Adjust free chlorine / shock — always the last step, and always done after other parameters are in range
Testing your water
Test free chlorine and pH at minimum twice weekly during Florida summer. Test alkalinity, calcium hardness, and CYA monthly. After any significant rain event or heavy bather load, test before assuming chemistry is still in range — conditions change quickly.
Home test kits (Taylor K-2006 or similar drop-based kits) provide more accurate results than test strips for serious chemistry management. Test strips are convenient for quick checks but are less precise for parameters like CYA and calcium hardness. Professional water testing (which every service visit includes) gives you the most accurate results and should form the foundation of your chemistry record.
Never mix chemicals
This is the most important safety rule in pool chemistry: never mix chemicals directly with each other, and never add multiple chemicals to the pool simultaneously. Some combinations — particularly chlorine and acid — react violently and produce toxic gases. Add one chemical at a time, always pre-dissolve granular products in a bucket of water before adding to the pool, allow each addition to fully circulate before testing or adding anything else, and store different chemicals in separate, clearly labeled containers well apart from each other.