Pool Water Testing Basics: What to Check and How to Fix It

Balanced pool water is the foundation of a clean, safe, and comfortable swimming experience. It also protects your pool shell, equipment, and surfaces from damage that can be expensive to repair. The good news is that water chemistry is not complicated once you understand what you are looking at.

This guide covers the six most important things to test, the ranges you are aiming for, and what to add when your numbers are off.

For most residential pools, testing two to three times per week during swim season is the right cadence. After heavy rain, a large pool party, or any chemical addition, test again before the next swim. A simple dip-strip test takes about 30 seconds and gives you a quick read on the most critical values.

For a more accurate picture, use a liquid test kit or take a water sample to your local pool supply store for a full analysis every few weeks.

Ideal range: 1.0 – 3.0 ppm

Chlorine is your primary sanitizer — it kills bacteria, algae, and other contaminants. Free chlorine is the active, usable form in your water.

Too low (below 1.0 ppm): Add chlorine shock or granular chlorine. Liquid chlorine (sodium hypochlorite) works quickly for a fast correction. Stabilized chlorine tablets (trichlor) are good for routine maintenance via a floater or feeder.

Too high (above 5.0 ppm): Stop adding chlorine and allow sunlight to naturally burn it off. Do not swim until levels drop below 3.0 ppm.

Ideal range: 7.4 – 7.6

pH measures how acidic or basic your water is. It is the most important value to keep in range because it affects how well chlorine works and how comfortable the water feels on skin and eyes.

Too low (below 7.2 — acidic): Add sodium carbonate (soda ash) to raise pH. Acidic water corrodes equipment, irritates eyes and skin, and can damage your pool surface over time.

Too high (above 7.8 — basic): Add muriatic acid or sodium bisulfate (dry acid) to lower pH. High pH reduces chlorine effectiveness and can cause cloudy water and scale buildup.

Ideal range: 80 – 120 ppm

Total alkalinity (TA) acts as a buffer for pH — it keeps pH from swinging up and down dramatically. If your alkalinity is off, pH becomes very difficult to stabilize.

Too low (below 80 ppm): Add sodium bicarbonate (baking soda). Low alkalinity causes pH to bounce around unpredictably.

Too high (above 120 ppm): Add muriatic acid in small doses with the pump running. High alkalinity makes it hard to lower pH and can contribute to cloudy water.

Ideal range: 200 – 400 ppm (fiberglass pools can run on the lower end of this range)

Calcium hardness measures the amount of dissolved calcium in your water. Too little and the water becomes aggressive, pulling calcium from surfaces and equipment. Too much and you get scale deposits on the shell, waterline, and plumbing.

Too low (below 150 ppm): Add calcium chloride to raise hardness. This is especially important for concrete pools; fiberglass pools are more forgiving but still benefit from staying in range.

Too high (above 500 ppm): There is no chemical to lower calcium hardness — the only fix is to partially drain and refill with fresh water. This is why it is important not to over-correct when raising it.

Ideal range: 30 – 50 ppm

Cyanuric acid (CYA) protects chlorine from being broken down by UV sunlight. Without it, chlorine in an outdoor pool can be depleted within hours on a sunny day.

Too low (below 20 ppm): Add cyanuric acid (stabilizer) directly to the pool. Dissolve it in a bucket of warm water first for faster distribution.

Too high (above 80 ppm): High CYA reduces chlorine effectiveness significantly — a condition sometimes called chlorine lock. The only reliable fix is a partial drain and refill. Avoid over-stabilizing by not relying exclusively on stabilized chlorine tablets (trichlor) as your only chlorine source.

Ideal range: below 1,500 ppm (some sources say up to 2,000 ppm is acceptable)

TDS measures everything dissolved in your water — minerals, chemicals, debris, and byproducts of sanitation. Over time, TDS climbs as you add chemicals and water evaporates.

Too high: There is no chemical fix. A partial drain and refill is the only way to bring TDS down. High TDS can make water look dull, reduce chemical effectiveness, and cause equipment issues.

1. Test free chlorine and pH every 2–3 days
2. Adjust pH first — it affects how well everything else works
3. Check alkalinity weekly and adjust before adjusting pH if it is off
4. Test calcium hardness and CYA monthly
5. Run your pump at least 8 hours per day to keep water circulating

When multiple values are off, fix them in this order: alkalinity first, then pH, then chlorine. Alkalinity stabilizes pH, and pH affects how effective chlorine is. Jumping straight to chlorine when pH is off is like mopping the floor before fixing a leak.

If you have questions about your specific pool or want a professional water analysis, contact us — we are happy to help.