A North Texas pool stays clear when five readings sit in their target ranges, and calcium is the one our hard water keeps pushing up. The targets are pH 7.4 to 7.6, total alkalinity 80 to 120 ppm, calcium hardness 200 to 400 ppm, cyanuric acid (CYA), sold as stabilizer, 30 to 50 ppm (60 to 80 on salt), and free chlorine set against that CYA.
The numbers matter because they fail together. Let them drift and you get algae, cloudy water, stinging eyes, or scale on your tile, and chasing one number without the others in place creates a loop.
The five numbers that matter
The five target ranges below come from published guidance, not house rules. They follow the CDC’s guidance for home pools for sanitizer and pH, and the ANSI/APSP/ICC-11 water quality standard and the Pool & Hot Tub Alliance’s water chemistry guidelines for alkalinity, calcium, and stabilizer. The sanitizer-specific alkalinity split below comes from the PHTA Recreational Water Quality Committee’s Total Alkalinity in Pool and Spa Water, which is the only one of the three that addresses electrolytic chlorine generators directly. Where we narrow a published range, we say so and explain why.
| Reading | Ideal range | What it controls |
|---|---|---|
| Free chlorine | At least 7.5% of your cyanuric acid (5% on salt): 2 to 4 ppm at 30 to 50 ppm CYA, 6 ppm at 80 | Sanitizer that kills algae and bacteria |
| pH | 7.4 to 7.6 | How well chlorine works and how the water feels |
| Total alkalinity | 80 to 120 ppm | Buffer that keeps pH stable |
| Calcium hardness | 200 to 400 ppm | Protects surfaces; too high causes scale |
| Cyanuric acid | 30 to 50 ppm, or 60 to 80 ppm on a salt pool | Shields chlorine from sunlight |
Free chlorine: the sanitizer
Free chlorine is what keeps your water safe. It kills bacteria and algae and breaks down the organic gunk that swimmers, leaves, and storms bring in. The CDC recommends a minimum of 1 ppm free chlorine in a pool at all times, and at least 2 ppm in a pool that uses cyanuric acid. That covers nearly every pool in this area, including yours if you run stabilizer or use dichlor or trichlor tablets.
Treat that 2 ppm as a floor rather than a target. The working range is 2 to 4 parts per million for a pool holding stabilizer at the 30 to 50 ppm this guide recommends.
That range moves with your stabilizer, though, because cyanuric acid holds chlorine back as well as protecting it. The floor is roughly 7.5 percent of your cyanuric acid reading on a chlorine pool, or about 5 percent behind a salt cell. At 40 ppm of stabilizer that floor is about 3 ppm of free chlorine on a chlorine pool. At 80 ppm, where a salt pool is run, it is 4 ppm behind a cell and 6 ppm on a chlorine pool. A pool carrying 2 ppm at that level is not adequately sanitized on either, even though the test strip looks fine.
So a chlorine reading only means something next to a cyanuric acid reading. If yours has climbed past the useful range, the arithmetic and the way back down are in what to do about high cyanuric acid.
In a Plano summer, lean toward the high end. Heat and sunlight burn chlorine off quickly, so a level that looked fine in the morning can be near zero by evening. The most common cause of a green pool is chlorine that dipped too low for a day or two. If that has already happened to you, our green-to-clean guide covers the recovery.
pH and its buffer, total alkalinity
If you only learn to manage one number, make it pH. The CDC sets the band at 7.0 to 7.8 because that range “best balances killing germs to prevent swimming-related illness, the lifespan of the pipes, and swimmers’ comfort.” Those are three jobs on one dial, and they fail in opposite directions. As pH climbs, chlorine gets worse at killing germs, especially above 8.0; below 7.0, chlorine kills faster but the water starts eating your pipes and equipment.
We target 7.4 to 7.6, near the middle, because it leaves room to drift in either direction between weekly visits without leaving the safe range.
- pH too low (acidic, below 7.2): the water corrodes metal fittings, heater parts, and pump seals, and it stings eyes and skin.
- pH too high (above 7.8): chlorine becomes sluggish and inefficient, water turns cloudy, and scale starts forming, a real risk once calcium has built up.
At a pH of 8.0 much of your chlorine is barely sanitizing, and pouring in more won’t help until pH comes down. Fix pH first, then judge your chlorine.
Total alkalinity is the shock absorber for pH. The ANSI/APSP-11 standard allows a wide band, 60 to 180 ppm, but narrows the ideal to match your sanitizer. Salt systems and liquid or cal hypo chlorine push pH up, so they want roughly 80 to 100 ppm. Tablets pull it down, and dichlor slightly, so they want 100 to 120 ppm.
Keep total alkalinity in the 80 to 120 ppm range that spans both and your pH stays put. Let it drop too low and pH starts bouncing around unpredictably with every rain and every chemical addition, which is called pH bounce. Set alkalinity before you fine-tune pH, because alkalinity is what holds pH steady.
Calcium hardness and the North Texas problem that creeps up on you
Calcium hardness is the number that surprises new DFW pool owners. The North Texas Municipal Water District, which supplies much of Collin County, describes its treated water as moderately hard and attributes the mineral content to Lavon Lake. That’s harmless in drinking water, but in a pool it compounds: the water evaporates, the calcium stays behind, and every summer top-off adds more. After a few seasons the number has only gone one direction.
Target 200 to 400 ppm calcium hardness, the Pool & Hot Tub Alliance’s ideal range for pools. Its tolerated band is wider, 150 to 1,000 ppm. The guidelines split calcium by vessel, pools versus spas, not by surface material, so don’t aim a vinyl-liner or fiberglass pool at a spa range. The two failure modes:
- Too low: the water gets aggressive and pulls calcium out of plaster, grout, and concrete surfaces, etching them over time.
- Too high, combined with high pH: calcium falls out of solution and forms that crusty white scale on your tile line and inside your heater and pipes. This is the most common chemistry complaint we see in Plano, and it has its own guide in hard water and your pool.
Diluting is what brings calcium down, and because our fill water is already hard, it takes more replaced water than the simple ratio suggests. How much, and how to replace it safely in this soil, is in draining a pool in Collin County clay.
Watch the tile line for early scale
A faint white, chalky crust forming at the waterline is your early warning that calcium and pH are climbing together. Catch it there and a chemistry adjustment fixes it. Ignore it for a season and you’re looking at a bead-blasting or acid treatment to get it off.
Cyanuric acid: sunscreen for your chlorine
Cyanuric acid protects free chlorine from the Texas sun. Without it, the intense summer sun destroys free chlorine within hours. With the right amount, your chlorine lasts through the day. Target 30 to 50 ppm, which is the ideal range in the ANSI/APSP-11 standard.
A salt pool is the exception and is run higher, at 60 to 80 ppm, because the cell makes chlorine in small continuous amounts that need more protection to survive the afternoon. The maximum is left to local code, which the PHTA guidelines say is “typically 100 ppm,” and in our experience a Texas pool that reaches it is already losing the fight against algae.
More stabilizer isn’t better, though:
- Too little (below 30): the sun burns your chlorine off by midday and you fight a losing battle against algae.
- Too much (past your target, and certainly above 80): the more stabilizer in the water, the higher you have to push your chlorine for the same sanitizing power. Past a point that level becomes impractical to hold, so algae can take off while your test still shows some chlorine. The fix is usually replacing part of the water.
Cyanuric acid creeps up over time, especially if you use stabilized chlorine tablets, because every tablet adds a little more. It’s worth testing a few times a season so it doesn’t sneak past the useful range.
The order you adjust things in
Adjust in this order, because each number affects the next:
| Step | Adjust | Why first |
|---|---|---|
| 1 | Total alkalinity | Stabilizes pH so the next steps hold |
| 2 | pH | Makes chlorine effective and protects equipment |
| 3 | Calcium hardness | Prevents etching and scale |
| 4 | Cyanuric acid | Protects chlorine from sunlight |
| 5 | Free chlorine | Now it can do its job |
Add chemicals one at a time, and slowly
Never mix pool chemicals together or pour several in at once. Add one, let the pump circulate it for a few hours, then re-test before adding the next. Dumping chemicals in quickly is how people overshoot, cloud the water, or create dangerous reactions. How each product should be handled and stored between doses is in pool chemical safety and storage.
This same order applies after anything that dilutes the pool, which in North Texas usually means a storm. Alkalinity first is the part people skip, and the reason it matters most then is in your pool after a heavy rain.
How often to test
The CDC standard is to test free chlorine and pH at least twice a day, and more often when a number of people are swimming. That’s written for the worst case, and few homeowners do it.
What we see work in a Plano summer is testing chlorine and pH every couple of days, plus after every storm and every heavy pool party, which are the two events that most often start a bloom. Check alkalinity, calcium, and cyanuric acid every couple of weeks. In the cooler months you can ease off, since algae growth and chlorine burn-off slow with the temperature.
If keeping five numbers in range every week sounds like a part-time job, that’s close to what it is in our climate, and it’s what a weekly service plan takes off your plate. We test and balance every visit and leave you the readings in a photo report, so the chemistry is handled and you get to swim. You can compare weekly and biweekly schedules here or reach out for a quote.
