Pool Water Chemistry Basics: the 5 Numbers That Matter
No chemistry degree required -- just five numbers, tested weekly, changed one at a time. Plus the Orange County hard-water angle nobody warns you about.
Serving Orange County, CA · Upfront pricing · No chemistry degree needed
The five numbers
| Number | Target | Too low | Too high |
|---|---|---|---|
| Free chlorine (sanitizer) | 1-3 ppm | Algae, cloudy water, unsafe water | Bleached swimsuits, irritated eyes/skin |
| pH (acidity) | 7.2-7.6 | Corrodes equipment, etches plaster | Scale, cloudy water, chlorine stops working well |
| Total alkalinity (pH buffer) | 80-120 ppm | pH swings wildly ("pH bounce") | Hard to move pH down; scale risk |
| Calcium hardness | 200-400 ppm | Etches plaster, pits surfaces | Scale on tile and equipment -- the OC special |
| Cyanuric acid (stabilizer) | 30-50 ppm | Sun burns off chlorine in hours | "Chlorine lock" -- chlorine present but ineffective |
Test weekly with a drop-based kit. Change ONE thing at a time and give adjustments 24 hours -- chasing numbers with chemicals is how one drifting number becomes three problems.
The Orange County hard-water angle
OC tap water arrives at 200+ ppm calcium in many cities, and two forces push it higher all year: evaporation (water leaves, calcium stays) and top-offs (every refill adds another 200+ ppm). Left alone, hardness creeps toward 800-1,000 ppm -- and that's when tile lines crust, heaters scale, and water goes cloudy no matter how much you shock it.
- Monthly sequestering agent: $15-25/month in product keeps calcium dissolved instead of deposited. The cheapest insurance in OC pool chemistry.
- Watch the pH-calcium combo: high pH + high hardness = scale. Keep pH in the low 7s and the same hardness number causes far fewer problems.
- Partial drain every 3-5 years: dilution is the only real removal. Schedule it for winter/early spring; drain to the sewer cleanout per city rules.
- After a green episode: the algae is gone but the scale it hid behind is suddenly visible. Our green pool cleanup page covers the hard-water assessment we run before quoting -- and tile calcium removal covers the fix when scale has already won.
The weekly routine (15 minutes)
- Test all five numbers with the drop kit; write them down (trends beat snapshots).
- Adjust ONE thing -- usually chlorine or pH first. Alkalinity before pH if both are off (alkalinity is the buffer; fix the buffer, then the number).
- Brush the walls -- circulation plus brushing beats chemicals alone for distribution.
- Check the skimmer and pump baskets; a starved pump throws every number off.
- Re-test in 24 hours. If a number keeps drifting the same direction every week, that's a diagnosis (leak, over-stabilization, failing cell) -- not a dosing problem.
Salt pools: same five numbers, same weekly test. The cell makes chlorine; it doesn't manage the other four -- and cell aeration pushes pH up faster, so salt owners usually dose acid more often.
For the full cost picture, see the ultimate guide to pool service in Orange County.
Frequently asked questions
How often should I test my pool water?
Weekly with a drop-based test kit -- the full panel: free chlorine, pH, total alkalinity, calcium hardness, cyanuric acid. Test strips are fine for spot checks between, but they're a screening tool, not a management tool. After any big event (storm, Santa Ana winds, a pool party), test again.
Why is my pH always high in Orange County?
Three OC drivers: hard, alkaline fill water; aeration from spillovers, waterfalls, and salt-system cells (aeration drives pH up); and plaster pools, which push pH up for their first year or two. It's normal here to add muriatic acid regularly -- the fix isn't fighting it once, it's expecting it weekly.
What's the cheapest way to lower calcium hardness?
Partial drain and refill -- dilution is the only practical way to remove dissolved calcium (sequestering agents hold it in solution; they don't remove it). In OC, plan on a partial drain every 3-5 years as hardness creeps from 200+ ppm fill water toward the 800-1,000 ppm problem zone. Check your city's discharge rules: drain to the sewer cleanout, never the street.
Do saltwater pools need less chemistry testing?
No -- salt pools need the SAME five numbers, tested just as often. The salt cell makes chlorine from salt; it doesn't manage pH, alkalinity, hardness, or stabilizer. Salt pools actually drift pH upward faster (cell aeration), so they often need more acid attention, not less.
My water is clear but the tile line is crusty and the heater is scaling -- what's wrong?
High calcium hardness plus high pH -- the classic OC hard-water combo. Clear water with scale means the chemistry is precipitating calcium onto surfaces instead of holding it dissolved. Lower pH to range, add a sequestering agent monthly, and plan a partial drain if hardness is above 800 ppm. Our green pool cleanup page covers the post-algae hard-water assessment; tile-scale specifics are on our calcium removal page.
Rather not own the chemistry?
Weekly service means the five numbers are our problem -- tested, logged, and balanced every visit.
Get a free, no-pressure quote
Send us photos of your pool and we'll quote your cleanup price.