Pool Care Blog
Pool Chemistry 101: What Every Houston Pool Owner Should Know
Chemistry · January 28, 2026 · 7 min read
Pool chemistry can feel overwhelming — pH, alkalinity, CYA, calcium hardness, TDS, phosphates. It reads like a college lab report. But at its core, pool chemistry comes down to just two goals: keep the water safe to swim in and keep it from destroying your equipment. Here's the plain-English breakdown.
Chlorine: Your First Line of Defense
Chlorine is the sanitizer that kills bacteria, viruses, and algae. Without adequate chlorine, your pool becomes a petri dish within hours. The ideal range is 2–4 ppm (parts per million) of free chlorine. Below 1 ppm, algae can start growing. Above 5 ppm, and swimmers may experience skin and eye irritation.
In Houston's intense UV environment, unprotected chlorine can be destroyed by sunlight in as little as 2 hours. That's where CYA comes in.
CYA (Cyanuric Acid): Chlorine's Sunscreen
CYA acts as a UV shield for your chlorine. The ideal range is 30–50 ppm for pools using liquid chlorine, and 60–80 ppm for saltwater pools. Here's the catch: CYA doesn't evaporate or break down — it only leaves the pool when water is drained or diluted. Over time, CYA accumulates, and high CYA levels (above 100 ppm) actually make chlorine less effective. This is one of the most common issues we see in Houston pools.
Pro Tip: The CYA-Chlorine Relationship
Your free chlorine should be roughly 7.5% of your CYA level to remain effective. If your CYA is at 80 ppm, you need at least 6 ppm of free chlorine to fight algae. Most pool store recommendations don't account for this — which is why pools with "perfect" chlorine levels still turn green.
Technician Tip
Houston pool store water tests often read low on CYA because their reagents expire in our heat. Bring a sealed water sample in a clean plastic bottle — and get a second opinion if CYA reads below 30 ppm. We see this misread constantly.
pH: The Comfort & Corrosion Factor
pH measures how acidic or basic your water is on a scale of 0–14. The ideal range for pools is 7.4–7.6 — slightly above neutral (7.0). This range matches the pH of human tears, which is why properly balanced water feels comfortable on eyes and skin.
Low pH (below 7.2) causes water to become corrosive — it'll eat through metal heat exchangers, erode plaster, and destroy equipment seals. High pH (above 7.8) causes chlorine to lose effectiveness and leads to calcium scaling on tile and equipment.
Alkalinity: The pH Stabilizer
Total alkalinity (80–120 ppm) acts as a buffer for pH. Think of it as the shock absorber that prevents pH from swinging wildly up and down. If your pH is constantly drifting despite corrections, your alkalinity is likely off. Always adjust alkalinity first, then pH.
Calcium Hardness: Protecting Your Surfaces
Calcium hardness (200–400 ppm) prevents your water from becoming "hungry" for calcium. Low calcium water will pull calcium from your pool's plaster, causing etching, roughness, and eventual structural damage. High calcium leads to cloudy water and scale deposits. Houston's tap water tends to run on the harder side, so this is less of an issue for most local pools.
Why Pool Store Tests Can Be Misleading
Pool stores use test strips or DPD-based tests that measure total chlorine, not free chlorine. Total chlorine includes combined chlorine (chloramines) — the stuff that makes your eyes burn and smells like "chlorine." Combined chlorine is actually used-up chlorine that's no longer sanitizing your water. A pool store might tell you your chlorine is "fine" at 3 ppm total, but if 2 ppm of that is combined chlorine, you only have 1 ppm actually working. We use FAS-DPD testing that differentiates the two.
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