The 5-9 Hydrion Lo Ion test kit will give accurate pH readings at each 0.5 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. Lo Ion Kits give accurate readings in dilute or unbuffered solutions where in indip and read in in tests may read low. Estimates can be made to 0.25 ph units.