From: Low-cost, disposable colourimetric sensors for metal ions detection
Ca(II) (mg/L) | Mg(II) (mg/L) | M | °F | |
---|---|---|---|---|
Very soft | 6 | 1 | 1.9 × 10− 4 | 2 |
Soft | 18 | 4 | 6.1 × 10− 4 | 6 |
Medium | 30 | 6 | 1.0 × 10− 3 | 10 |
Hard | 45 | 9 | 1.5 × 10− 3 | 15 |
Very hard | 70 | 15 | 2.4 × 10− 3 | 24 |
Extremely hard | 100 | 20 | 3.3 × 10− 3 | 33 |