The concentration of a coolant is indicated by pH which is the chemical measurement of acidity or alkalinity. A pH of 1 would indicate a strong acid, of 13 a strong alkali, 7 is neutral.
This is a logarithmic scale. Each number is 10 times stronger or weaker than the number next to it. A pH of 9 is 10 times more alkaline as a pH of 8. A pH of 10 is 100 times more alkaline as a pH of 8.