Alkalinity is measured by titrating a given sample with 0.02N sulphuric acid. For highly alkaline sample, the first step is titrating to a pH of 8.3. This is known as the phenolphthalein alkalinity and measures the amount of hydroxide and half the carbonate that is present. Phenolphthalein indicator change from pink to colorless at pH 8.3. The second step is titrating to a pH of 4.5, the indicators used are methyl orange ( orange at pH 4.6 ) . This is the total alkalinity and measures the alkalinity due to hydroxide, carbonates, and bicarbonates