What is the reason of white turbidity when measuring hardness with EDTA?

There are a lot of bicarbonate in water, and calcium carbonate precipitates under alkaline conditions. The solution is: after measuring the water sample, add 1-2 drops 1: 1 hydrochloric acid, heat and boil, and the bicarbonate decomposes to generate carbon dioxide to escape, cool to 50-60 degrees, add indicator and buffer solution, and then titrate.