Pool chlorine levels chart: what your readings mean
You tested your water. Now you're staring at a number and wondering: is that good? Here's a straightforward chart covering every chlorine-related reading and what to do about it.
Free chlorine (FC) levels
Free chlorine is the active sanitizer in your pool — the chlorine that's available to kill bacteria and algae. This is the most important number on your test.
| FC Level (ppm) | Status | Action |
|---|---|---|
| 0 | No sanitizer | Add chlorine immediately. Your pool has no protection against bacteria or algae |
| 0.1 – 0.9 | Dangerously low | Add chlorine now. Water is not safe for swimming |
| 1.0 – 1.9 | Low | Acceptable short-term, but raise to 2+ ppm soon |
| 2.0 – 4.0 | Ideal | No action needed. This is your target range |
| 4.1 – 7.9 | High | Let it drop naturally. Avoid swimming above 5 ppm |
| 8.0+ | Too high | Do not swim. Wait for FC to drop below 5 ppm before using the pool |
CYA changes everything
The 2–4 ppm range assumes low or no cyanuric acid (CYA). If you use stabilized chlorine or have CYA in your water, your FC target should be higher. A common guideline is to keep FC at about 7.5% of your CYA level. So at CYA 50, aim for FC of 3–4 ppm. At CYA 80, aim for 6+ ppm.
Combined chlorine (CC) levels
Combined chlorine is chlorine that's already reacted with contaminants — it's spent and no longer sanitizing. You calculate it by subtracting FC from TC.
| CC Level (ppm) | Status | Action |
|---|---|---|
| 0 – 0.2 | Excellent | No action needed |
| 0.2 – 0.5 | Normal | Acceptable. Monitor on next test |
| 0.5 – 1.0 | Elevated | Consider shocking soon if this persists |
| 1.0+ | High | Shock the pool. Chloramines are building up |
High combined chlorine is what causes "that pool smell." It also irritates eyes and skin. If CC stays above 0.5 ppm across multiple tests, it's time to shock.
Total chlorine (TC) levels
Total chlorine is simply FC + CC. On its own, TC doesn't tell you much — what matters is how close it is to your free chlorine reading.
| Scenario | What It Means | Action |
|---|---|---|
| TC equals FC | No combined chlorine. All your chlorine is active | Nothing — this is perfect |
| TC slightly above FC | Small amount of CC. Normal after heavy use | Monitor. Shock if it persists |
| TC much higher than FC | High CC. Chloramines are building up | Shock immediately |
When to test chlorine
- Routine: 2–3 times per week during swim season
- After heavy use: Pool parties, lots of swimmers, heavy rain
- After shocking: Test the next day to confirm FC has dropped to safe levels
- After adding chemicals: Wait at least 30 minutes with the pump running, then retest
Factors that affect chlorine levels
Chlorine doesn't stay at a fixed level — several things consume or degrade it:
- Sunlight (UV): Destroys free chlorine rapidly. An unprotected pool can lose 90% of its FC in a few hours of direct sun
- CYA (stabilizer): Shields chlorine from UV breakdown. Essential for outdoor pools, but too much reduces chlorine effectiveness
- Bather load: Sweat, sunscreen, and body oils consume FC fast
- Temperature: Warmer water breeds bacteria faster, which uses up chlorine more quickly
- Algae: Even a small bloom will consume chlorine rapidly
The CYA/chlorine relationship
CYA protects chlorine from sunlight, but it also binds to chlorine and slows it down. The higher your CYA, the more FC you need to maintain effective sanitization. This is why tracking both numbers together matters — a "good" FC reading can actually be too low if your CYA is high.
Quick reference: ideal ranges
| Reading | Ideal Range | Test Frequency |
|---|---|---|
| Free Chlorine (FC) | 2 – 4 ppm (adjust for CYA) | 2–3x per week |
| Combined Chlorine (CC) | Below 0.5 ppm | Every test (calculated from FC and TC) |
| Total Chlorine (TC) | Should be close to FC | 2–3x per week |
| Cyanuric Acid (CYA) | 30 – 50 ppm | Monthly |
Track your chlorine levels over time
PoolChem Tracker logs FC, TC, and CC together, calculates dynamic FC targets based on your CYA level, and shows you trends so you can spot problems before they start.
Keep reading
- Free Chlorine vs Total Chlorine: What's the Difference? — a deeper dive into the three types of chlorine
- Pool Chemistry for Beginners: The 5 Numbers That Matter — chlorine is just one piece of the puzzle
- How Often Should You Test Your Pool Water? — a realistic testing schedule that actually works