Rellena los espacios en blanco para completar el texto.
Fill in the blanks to complete the following passages about how hard water can be made soft.
METHOD 1 - hardness can be removed by . When heated, the calcium decomposes to form calcium , which is the that affects heating systems. This method does not apply to hard water.
METHOD 2 - Both types of hardness can be removed by adding ( , or Na₂CO₃) to the water. The reacts with the calcium and ions to form an precipitate of calcium and magnesium . The ions are no longer in the water, so they are unable to make it hard.
METHOD 3 - Both types of hardness can be removed by running the hard water through ' ' columns. The columns have lots of (or hydrogen) ions, and '' them for calcium or ions in the water.