How to Read Your Pool Water Test Results — Frisco Guide

The five numbers that matter on every pool water test are: free chlorine (target 2-4 ppm), pH (target 7.2-7.4), total alkalinity (target 70-90 ppm in Frisco's hard water), cyanuric acid (target 30-50 ppm), and calcium hardness (target 200-400 ppm). If those five are in range, your pool is safe and clear — everything else on the printout is secondary.

Most Frisco pool owners can't read their own water test results, which means they can't tell when the pool store is solving a real problem versus selling products they don't need. Here's every number on that test strip, what it means for Frisco's specific water conditions, and what to actually do when a number is off.

The Big Five: Numbers That Matter Every Week

1. Free Chlorine (FC)

What it is: The amount of active, available chlorine in the water that's ready to kill bacteria and algae.

Target range: 2-4 ppm (parts per million)

What it means when it's low (below 2 ppm): The pool is unprotected. Algae can establish, bacteria can survive, and the water will start going green within 24-48 hours in summer.

What it means when it's high (above 5 ppm): The pool was recently shocked or over-chlorinated. Not dangerous for the pool, but can irritate eyes and skin. Wait for it to drop below 5 ppm before swimming.

Fix when low: Add liquid chlorine. For a 15,000-gallon pool, 1 gallon of liquid chlorine raises FC by approximately 5-6 ppm.

Frisco note: In summer, UV burns through chlorine faster. If your FC drops below 2 ppm within 24 hours of your last chlorine addition, your CYA (stabilizer) is probably too low — chlorine has no UV protection.

2. pH

What it is: How acidic or basic the water is, on a scale of 0-14. Pool water should be slightly above neutral (7.0).

Target range: 7.2-7.4

What it means when it's low (below 7.0): The water is acidic. It corrodes metal components (heater heat exchanger, pump internals, handrails), etches plaster, and irritates eyes and skin. Acidic water destroys equipment faster than anything else.

What it means when it's high (above 7.6): The water is too basic. Chlorine becomes less effective (at pH 8.0, chlorine loses ~75% of its killing power), calcium precipitates out of solution and scales surfaces and equipment, and the water can cloud.

Fix when low: Add sodium carbonate (soda ash) or sodium bicarbonate (baking soda). Both raise pH — soda ash raises it faster.

Fix when high: Add muriatic acid. For a 15,000-gallon pool, 1 cup of muriatic acid lowers pH by approximately 0.1-0.2.

Frisco note: pH in Frisco pools tends to drift UP constantly because of the alkaline tap water, water feature aeration, and salt cell operation (if applicable). Plan on adding acid weekly. If your pH is consistently at 7.2 without acid additions, something is wrong — usually low alkalinity.

3. Total Alkalinity (TA)

What it is: The water's ability to resist pH changes. Think of it as pH's shock absorber. Higher alkalinity means pH changes slowly. Lower alkalinity means pH swings rapidly.

Target range: 70-90 ppm (for Frisco's hard water — lower than the 80-120 ppm you'll see in generic guides)

What it means when it's low (below 60 ppm): pH bounces wildly — hard to control, swings from high to low with small chemical additions. This is frustrating to manage and hard on equipment.

What it means when it's high (above 120 ppm): pH locks high and resists acid additions. You add acid, pH drops temporarily, then bounces right back to 7.8 within hours. High alkalinity also promotes calcium scaling — a major problem in Frisco's already-hard water.

Fix when low: Add sodium bicarbonate (baking soda). 1.5 pounds per 10,000 gallons raises TA by approximately 10 ppm.

Fix when high: Add muriatic acid. This lowers both TA and pH — you may need to aerate the pool afterward to raise pH back up while keeping TA lower.

Frisco note: We keep TA at 70-90 ppm in Frisco pools — lower than the textbook 80-120 ppm. Lower TA gives better pH control in our alkaline water and reduces calcium scaling. If the pool store tells you to raise TA to 120 ppm, they're using a generic recommendation that doesn't work well in Frisco's water chemistry.

4. Cyanuric Acid (CYA / Stabilizer)

What it is: A UV shield for chlorine. CYA molecules wrap around chlorine molecules and protect them from ultraviolet destruction. Without CYA, the Frisco sun destroys chlorine in 2-3 hours.

Target range: 30-50 ppm

What it means when it's low (below 20 ppm): Chlorine burns off too fast. You'll add chlorine and it'll be gone by afternoon. The pool can't hold a residual.

What it means when it's high (above 70 ppm): Chlorine is over-protected — it's locked up by the CYA and can't effectively kill algae and bacteria. At 100+ ppm, your chlorine is essentially disabled even though it tests at 3 ppm. This is the most common problem in Frisco pools using chlorine tabs.

Fix when low: Add granular cyanuric acid (stabilizer). 1 pound per 10,000 gallons raises CYA by approximately 12 ppm.

Fix when high: Partially drain and refill the pool. No chemical reduces CYA — only dilution works. See our complete guide on CYA and chlorine tabs.

5. Calcium Hardness (CH)

What it is: The concentration of dissolved calcium in the water. All water has some calcium — the question is how much.

Target range: 200-400 ppm

What it means when it's low (below 150 ppm): The water is "hungry" for calcium and will pull it from wherever it can — your plaster, your grout, your tile. Low-calcium water dissolves and etches plaster surfaces, causing premature roughness and degradation.

What it means when it's high (above 400 ppm): Calcium precipitates out of solution and deposits on everything — tile (white crusty scale), plaster (roughness), salt cell (reduced output), heater heat exchanger (reduced efficiency). High calcium is the #1 water chemistry problem in Frisco pools.

Fix when low: Add calcium chloride. 1 pound per 10,000 gallons raises CH by approximately 10 ppm. Rarely needed in Frisco — our tap water already carries 150-250 ppm calcium.

Fix when high: Partially drain and refill. Like CYA, no chemical removes calcium — only dilution works. See our guide on hard water in Frisco pools.

The Secondary Numbers: Test Monthly

Total Dissolved Solids (TDS)

What it is: Everything dissolved in the water — minerals, chemicals, organic compounds, metals. Every chemical you add increases TDS. Evaporation concentrates TDS.

Target range: Below 3,000 ppm (for non-salt pools)

When it's too high: Water quality degrades — cloudy appearance, chemical interactions become unpredictable, and surfaces stain more easily. At very high TDS (above 5,000 ppm), the only fix is a partial or full drain and refill.

Phosphates

What it is: A nutrient that algae uses for growth. Phosphates enter the pool from fill water, landscaping runoff, body products, and decomposing organic material.

What to know: Phosphates don't cause algae — inadequate chlorine causes algae. If your chlorine is maintained at 2-4 ppm, algae can't grow regardless of phosphate level. Pool stores push phosphate removers as a recurring sale ($25/month) that most pools don't need.

Metals (Iron, Copper)

What it is: Dissolved metals in the water — typically iron (from well water or corroded equipment) or copper (from algaecide use or corroded copper heat exchangers).

When it matters: If you see brown stains (iron) or green/blue stains (copper) on your plaster after shocking. High metal levels + oxidation from chlorine = metal stains. If metals are detected, add a metal sequestrant before shocking.

Salt (for salt pools only)

What it is: The sodium chloride concentration needed for the salt chlorine generator to produce chlorine.

Target range: 3,000-3,500 ppm (check your specific system's recommended range)

When it's low: The cell can't produce adequate chlorine. Add pool-grade salt.

When it's high: The water tastes salty and can accelerate corrosion of metal components. The only fix is dilution — partially drain and refill.

How to Test at Home vs the Pool Store

Pool store test: More accurate for CYA, calcium, and TDS (they use electronic testers). Good for monthly comprehensive checks. Bad for making real-time decisions — you have to drive there, wait, and drive back.

Test strips at home: Fast and convenient for FC, pH, and alkalinity — the three numbers you need to check weekly. Accuracy is ±10-20% which is fine for weekly maintenance decisions. Keep strips out of direct sunlight and humidity — store them inside, not in the pool shed.

Liquid test kits (Taylor K-2006): The gold standard for home testing. More accurate than strips for all parameters. Takes 5-10 minutes to run a full test. Worth the $60-80 investment if you maintain your own pool.

Our approach: Your weekly pool technician tests FC, pH, and alkalinity at every visit with professional-grade reagent tests. We test CYA, calcium, and TDS monthly. Every test result is documented in your service report — you always know what your water looks like.

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