I'm having trouble with my pool chlorine levels. The test shows zero chlorine, even though I'm using tabs, shocking regularly, and all other levels...pH, alkalinity, and cyanuric acid (at 50) are in range, no phosphates or nitrates either. Any idea why the chlorine isn't showing up?
-
You're one step from joining Swimming Pool Forum – Water Chemistry, Pool Equipment & Maintenance.
Create a free account to post, follow threads, and never miss an update. Sign up free →
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
Why Is my pool chlorine disappearing?
- Thread starter Ice bergz
- Start date
brav3heart
Member
- Joined
- Jul 19, 2025
- Messages
- 5
Could be the chlorine is tied up with contaminants or your test isnt picking up stabilized chlorine well, especially with cyanuric acid at 50. Sometimes high CYA can hide the real chlorine levels. Have you tried a different test kit or checked for combined chlorine buildup??I'm having trouble with my pool chlorine levels. The test shows zero chlorine, even though I'm using tabs, shocking regularly, and all other levels...pH, alkalinity, and cyanuric acid (at 50) are in range, no phosphates or nitrates either. Any idea why the chlorine isn't showing up?
Trick-Vague55
New member
- Joined
- Aug 18, 2025
- Messages
- 2
Possible a chlorine demand. Even though you're adding chlorine, it's getting used up by contaminants before it shows up on your test. This can happen if there's a buildup of organic matter or combined chlorine that needs to be oxidized. Have you tried testing for total chlorine vs. free chlorine? That can help pinpoint if it's all being "used up."
Chlorine doesn’t just “vanish” on its own, so when it disappears fast it usually means the pool has something eating it up. The first thing I always check is stabilizer. If your CYA is low, the sun will burn off free chlorine in a couple of hours. That’s one of the biggest reasons outdoor pools can’t hold a chlorine level. Stores like MavaquaDoc explain this a lot in their guides because people overlook it.
The other common issue is high chlorine demand. If the water has a bunch of organics, pollen, leaves, sunscreen, sweat, rain runoff, the chlorine gets used up sanitizing all that. Same thing happens if there’s early-stage algae that you can’t see yet. Chlorine gets wiped out immediately.
Also make sure your pH and alkalinity are in range. When those drift too high, chlorine becomes way less effective, so even if you add the right amount it feels like it “disappears.
The other common issue is high chlorine demand. If the water has a bunch of organics, pollen, leaves, sunscreen, sweat, rain runoff, the chlorine gets used up sanitizing all that. Same thing happens if there’s early-stage algae that you can’t see yet. Chlorine gets wiped out immediately.
Also make sure your pH and alkalinity are in range. When those drift too high, chlorine becomes way less effective, so even if you add the right amount it feels like it “disappears.
Good points above @Ice bergz, especially chlorine demand since your CYA at 50 is already in a workable range. Do an overnight chlorine loss test to see if something’s chewing it up. That usually tells the story pretty fast.