Hydrion pH Indicator Solution kits feature specially formulated concentrated indicator solutions and give accurate pH measurements in very dilute test solutions with low buffer capacity (less than 0.1% phosphate buffer). Just one drop of the indicator solution added to 4 ml. of sample solution will provide an accurate ph reading, displayed in bright easy to view colors. 5-9 Hydrion pH Short Range Indicator Solution will give accurate pH readings at each .5 pH unit from pH 5-9, and is excellent for measuring the pH of waste water, pure water, tap water, rain water and pond water. Colors will remain stable for delayed readings.