PPM (Parts Per Million) is a unit of measurement that expresses concentration - specifically, how many parts of one substance exist within one million parts of another substance. In pool and spa maintenance, PPM is the standard unit for measuring chemical concentrations in water.
Quick Reference
- Definition: Parts per million - concentration measurement
- Pool Use: Measuring chlorine, alkalinity, calcium hardness, and other chemical levels
- Conversion: 1 PPM = 1 mg/L (milligram per liter)
- Example: 3 PPM chlorine = 3 parts chlorine per 1 million parts water
Understanding PPM in Pool Chemistry
Think of PPM as a way to measure very small amounts. If you had a million marbles and 3 of them were red, you'd have 3 PPM red marbles. In your pool, if you have 3 PPM chlorine, that means there are 3 parts of chlorine for every million parts of water.
Common Pool Chemical PPM Ranges
| Chemical | Ideal Range (PPM) |
|---|---|
| Free Chlorine | 1-3 PPM |
| Total Alkalinity | 80-120 PPM |
| Calcium Hardness | 150-300 PPM |
| Cyanuric Acid | 30-50 PPM |
Pro Tip: PPM is the same as mg/L (milligrams per liter). So when you see 3 PPM chlorine, it's the same as 3 mg/L - just different ways of expressing the same concentration.
Why PPM Matters
Using PPM allows pool professionals and homeowners to:
- Precisely measure very small concentrations of chemicals
- Follow standardized testing procedures
- Communicate chemical levels consistently
- Maintain proper water balance for safety and comfort
Understanding PPM helps you interpret test results and make informed decisions about chemical additions to keep your pool or spa water properly balanced.