Total Chlorine (TC)
Total chlorine (TC) is the sum of free chlorine (FC) and combined chlorine (CC) — every chlorine molecule in your water, whether it's still actively sanitizing or already used up. On its own, TC is the least useful chlorine number; its value is in what it tells you when subtracted from FC.
The formula
Three chlorine numbers, one simple relationship:
Or, more usefully:
You test FC and TC on a kit. CC is the difference. The difference is the actionable number.
Target relationship
There's no fixed TC target the way there's an FC target. What matters is how close TC is to FC.
| TC vs FC | Status | What it means |
|---|---|---|
| TC = FC | Perfect | No combined chlorine; all chlorine is active |
| TC up to 0.5 ppm above FC | Normal | Minor CC; not a problem |
| TC 0.5–1.0 ppm above FC | High CC | Chloramines building; shock recommended |
| TC > 1.0 ppm above FC | Very high CC | Strong smell, irritation; shock now |
"My total chlorine is 3 ppm" is a misleading statement
A reading of TC = 3 ppm tells you nothing about whether your pool is safe. If FC is 3 and CC is 0, your pool is sanitized. If FC is 1 and CC is 2, your pool is barely sanitized and reeks of chloramines. Always split TC into FC and CC before deciding what's happening.
Why TC alone misleads
Many old test kits and strips only show "chlorine" as a single number — that number is total chlorine. This created decades of confusion about what's really happening in pool water.
- A high TC reading can hide low FC. A pool with TC of 4 ppm could have FC of 4 (great) or FC of 1 (bad). Same TC number; very different sanitization.
- "I added chlorine and the number went up" doesn't always mean what you think. If CC is rising along with FC, contaminants are still winning.
- Chloramines smell like chlorine but don't sanitize like it. A pool with high TC and high CC can smell strongly of chlorine while being undersanitized.
The fix is to always read FC and TC together — never one without the other. See free chlorine vs total chlorine for the full breakdown.
How TC is measured
Liquid test kits use a two-step process to measure TC:
- DPD-1 reagent measures free chlorine. The water sample turns pink.
- DPD-3 reagent is then added. It releases the combined chlorine, which reacts with the remaining DPD-1 to deepen the pink. The total color = total chlorine.
The FAS-DPD method works similarly but uses drop-count titration for both readings, giving precision that color-matching can't.
Test strips read both FC and TC on adjacent color pads, but the accuracy is poor enough that the difference (CC) is often within the error bars — meaning strips can hide a real chloramine problem behind ambiguous color matching. For chloramine diagnosis, a liquid kit is essential. See test strips vs liquid test kits for the comparison.
When to look at TC
Two situations where TC matters:
- Calculating CC. You can't get combined chlorine without subtracting FC from TC. This is the only daily-use case for TC.
- Validating breakpoint. After shocking, you want TC to converge with FC. Watching the gap close confirms the chloramines are gone.
If your only chlorine reading is TC (older strips, some commercial test panels), assume some portion is locked up as CC. Switch to a kit that reports FC and TC separately as soon as practical.
Want to...
Stop guessing what TC means
PoolChem Tracker stores FC and TC side by side, calculates CC automatically, and flags chloramine buildup before the smell shows up.
