Converting Data Table to List and vice versa

I don't know what's wrong. I have a SQL Statement and an adapter

 DataTable datTableCur = new DataTable();
            datTable = new DataTable();
            sqlCmd = new SqlCommand(@"SELECT DISTINCT [" + form1.getCol() + "] FROM [" + form1.getTableName3() + "]", connection);
            sqlDatAdapter = new SqlDataAdapter(sqlCmd.CommandText, connection);
            sqlDatAdapter.Fill(datTableCur);

Since the format is "float" in SQL I convert it to "Double" in C# and put every element of the column in a List

 List<Double> convertCol = new List<Double>();
            List<Double> convertedCol = new List<Double>();
            foreach (DataRow row in datTableCur.Rows)
            {
                convertCol.Add((double)row[0]);
            }

Now I want to check if the elements have "," and if that's the case I want to replace the "," with a ".", so I convert every single element into a String, check this case, replace the char, convert it back to Double and store it in another List

  String convertToString;
            Double storeDouble;
            Double convertBackToDouble;

            for (int i = 0; i < convertCol.Count; i++)
            {
                storeDouble = convertCol[i];
                convertToString = storeDouble.ToString("0.######");


                if (convertToString.Contains(","))
                {
                    convertToString.Replace(",", ".");
                    convertBackToDouble = Convert.ToDouble(convertToString);
                    convertedCol.Add(convertBackToDouble);

                }

                else 
                {
                    convertedCol.Add(convertCol[i]);

                }
            }

and now here's my problem. I want to put that back into a DataTable, and put that in a ListBoxbut that doesn't work. I get an ArgumentException and the error, that the input array is longer than the number of columns in the table.

datTable.Rows.Add(form1.getCol());

            for (int j = 1; j < convertedCol.Count; j++)
            {
                datTable.Rows.Add(convertedCol[j]);
            }

            form1.colList.DisplayMember = form1.getCol();
            form1.colList.ValueMember = "Column";
            form1.col.DataSource = datTable;