Understanding Chlorine Demand: Why Your Pool Uses More Than Expected
Introduction
Do you find yourself constantly adding chlorine to your pool but never quite hitting the right level? You might be dealing with something known as chlorine demand — and it’s more common than you think.
In this guide, we’ll explain what chlorine demand is, why it happens, and how to reduce it using Deep Blue’s expert-tested products and pool care strategies.
What Is Chlorine Demand?
Chlorine demand refers to the amount of chlorine required to remove contaminants and maintain a stable free chlorine level. When chlorine demand is high, your pool quickly “uses up” chlorine, leaving little available for sanitising.
Signs of High Chlorine Demand
- Free chlorine levels remain at 0 despite frequent dosing
- Strong chloramine (chemical) smells
- Cloudy or green water even after treatment
- Test results show combined chlorine (CC) above 0.5 ppm
Common Causes
- Heavy bather load (sweat, sunscreen, body oils)
- Organic debris (leaves, insects, grass)
- Algae outbreaks
- Rain, storms, or dust
- High cyanuric acid or TDS levels
Step-by-Step: How to Reduce Chlorine Demand
1. Shock the Pool
Use Deep Blue Chlorine Shock or Non-Chlorine Shock at double or triple the normal dose to oxidise built-up contaminants. Do this in the evening and run the pump overnight.
2. Clean Everything
Scrub walls, steps, and floors to loosen algae or bacteria. Vacuum the pool thoroughly. Clean or backwash your filter using Deep Blue Filter Cleaner.
3. Check and Balance Water
Imbalanced water makes chlorine work harder. Use Deep Blue Test Strips to check:
- pH: 7.2–7.6
- Alkalinity: 80–120 ppm
- Stabiliser: 30–50 ppm
4. Use Algaecide Preventatively
Apply Deep Blue Long-Life Algaecide weekly to prevent algae — one of the biggest chlorine consumers.
5. Don’t Mix Chlorine Types
Mixing cal-hypo and trichlor, for example, can cause instability. Stick to one system unless advised otherwise.
6. Remove Excess Stabiliser
If cyanuric acid is above 70 ppm, it can “lock” chlorine. Dilute with fresh water and retest.
Can Chlorine Demand Be Permanent?
No — but chronic issues often indicate poor circulation, filtration, or water quality. Solve the root cause to restore balance.
Helpful Tools from Deep Blue
- Shock granules in bulk sizes
- Stabiliser reducers
- Full testing kits with CC readings
Loyalty Perks
Earn points on all chlorine products and troubleshooting tools — redeem for filters, algaecides, and more.
Conclusion
Chlorine demand is frustrating — but fixable. With the right approach and help from Deep Blue, you can bring your chlorine levels back to normal and enjoy clean, sanitised water every day.
FAQs
What’s the difference between free and combined chlorine?
Free chlorine sanitises. Combined chlorine is “used up” and should be removed via shocking.
Do I need to drain my pool if chlorine doesn’t hold?
Only if stabiliser or TDS levels are too high. Test first, then decide.
Will shocking always fix chlorine demand?
In most cases, yes — especially when paired with good filtration and brushing.
Is high chlorine demand dangerous?
It can leave your pool unprotected, even if levels appear high. Treat quickly.
Should I switch to non-chlorine options?
You can, especially in spas or small pools. We offer oxygen-based alternatives that avoid chlorine lock entirely.
