You add chlorine, test an hour later, and it's already dropped. You shock the pool and it looks great — then two days later it's back to nothing. If this sounds familiar, you're not adding too little chlorine. Something is consuming it faster than it can keep up. Here's what's actually going on.
This is the most common culprit, especially for pools that were just opened or recently had a large water change. Without CYA to protect it, sunlight destroys unstabilized chlorine extremely fast — as much as 90% can be gone within a few hours of direct sun exposure.
Fix: Test your CYA. If it's below 30 ppm, add stabilizer (granular cyanuric acid) to bring it to 40-50 ppm. You'll be amazed how much longer your chlorine lasts.
Chlorine doesn't just sanitize water — it reacts with and destroys organic material: leaves, pollen, sunscreen, sweat, body oils, algae spores, and more. After a heavy rainstorm, a pool party, or a period of neglect, there's so much organic material in the water that chlorine gets consumed almost instantly trying to deal with it all.
Fix: Shock aggressively at 2-3x normal dose. This is called "breakpoint chlorination" — you need to add enough chlorine to overwhelm all the organic demand and still have free chlorine left over. Run the filter continuously after shocking.
💡 The smell of chlorine doesn't mean you have too much — it means you have too little. That "pool smell" is actually chloramines, the byproduct of chlorine reacting with contaminants. A well-chlorinated pool has almost no smell.
At pH 8.0, chlorine is only about 20% as effective as at pH 7.4. Your test strip might show 3 ppm of chlorine, but that chlorine is barely doing anything. The result looks like chlorine that won't hold — but it's really chlorine that's being wasted because pH is too high.
Fix: Test pH. If it's above 7.6, lower it with muriatic acid before adding more chlorine.
You can have an algae problem before your pool turns green. In the early stages, algae consumes chlorine rapidly but isn't visible yet. If your chlorine keeps dropping and you can't explain it, test for algae by checking if the walls feel slippery or if the water has a slight greenish tint in certain light.
Fix: Shock at 3x normal dose and add algaecide the following day.
If you have a salt water pool and chlorine keeps dropping, your salt cell might not be generating enough chlorine. Check the cell output percentage on your controller — if it's maxed out and chlorine still won't hold, the cell may need cleaning or replacement.
Fix: Inspect and clean the salt cell. Also verify salt levels are in range (2700-3400 ppm for most systems).
Here's a quick decision tree:
⚠️ Don't keep adding chlorine without diagnosing the cause. You'll waste money and potentially over-stabilize the water (too much CYA) or throw off other chemistry. Fix the root cause first.
Tell Wade your readings and he'll identify why your chlorine isn't holding and walk you through exactly what to do based on your specific pool setup.
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