How Water Chemistry Can Destroy Your Pool Heater
1. Low pH = Acidic Water = Corrosion
What happens: When your pH drops too low (below 7.2), your pool water becomes acidic. This acidic water aggressively attacks metal components, especially the copper heat exchanger found in most gas heaters.
How fast: If your water stays acidic, visible damage can happen in as little as a few weeks, especially with heat accelerating the reaction.
Signs of damage:
- Green or blue water (copper leaching into the water)
- Heater producing rust-colored stains or flakes
- Leaking from internal heater parts
2. High pH and High Calcium = Scale Buildup
What happens: High pH, high calcium hardness, or high total alkalinity causes calcium to fall out of solution and form scale on heater elements.
How fast: Scale can start forming within weeks and will build up layer by layer, insulating the heat exchanger and drastically reducing heat transfer.
Signs of damage:
- Heater not heating efficiently
- Overheating and shutting down
- White, crusty deposits on internal parts
3. Low Calcium Hardness = Soft Water = Etching and Corrosion
What happens: Water low in calcium hardness (under 150 ppm) becomes “soft,” and will draw calcium from wherever it can, including metal or even heater gaskets and seals.
How fast: Long-term exposure (1–3 months) can start breaking down parts, especially in gas heaters.
Signs of damage:
- Heater corrosion, especially around joints or gaskets
- Heater failures that seem unrelated to age or use
4. High Chlorine = Oxidation and Metal Damage
What happens: While chlorine sanitizes your pool, too much of it, especially when combined with low pH, can cause rapid oxidation and damage metal surfaces inside your heater.
How fast:Constant high chlorine levels (above 5 ppm) can start causing issues in under a month.
Signs of damage:
- Heater parts become brittle or pitted
- Leaks around heat exchanger
- Shortened life of electronic components
How to Protect Your Heater
- Test and balance water weekly
- Keep pH between 7.4–7.6
- Keep Total Alkalinity between 80–120 ppm
- Keep Calcium Hardness between 200–400 ppm
- Maintain proper chlorine levels (1–3 ppm for most pools)
- Ensure good flow through the system and clean filters regularly
Bottom Line
A pool heater can start showing damage from bad water chemistry in as little as a few weeks, and complete failure can occur in a few months. A little maintenance goes a long way. Regular testing and adjusting your chemistry is the cheapest insurance you can buy to protect your heater.
