Create Rx Tx

groundFungus:
Have you tried the PH example code (below) by itself and unmodified (except RX & TX pins)? Does it work?
Note that I change the RX and TX pins to the ones in your code (RX=7, TX=6).

//This code was written to be easy to understand.

//Modify this code as you see fit.
//This code will output data to the Arduino serial monitor.
//Type commands into the Arduino serial monitor to control the pH circuit.
//This code was written in the Arduino 1.8.3 IDE
//An Arduino UNO was used to test this code.
//This code was last tested 6/2017

#include <SoftwareSerial.h>                          //we have to include the SoftwareSerial library, or else we can't use it
#define rx 7                                          //define what pin rx is going to be
#define tx 6                                          //define what pin tx is going to be

SoftwareSerial myserial(rx, tx);                      //define how the soft serial port is going to work

String inputstring = "";                              //a string to hold incoming data from the PC
String sensorstring = "";                            //a string to hold the data from the Atlas Scientific product
boolean input_string_complete = false;                //have we received all the data from the PC
boolean sensor_string_complete = false;              //have we received all the data from the Atlas Scientific product
float pH;                                            //used to hold a floating point number that is the pH

void setup() {                                        //set up the hardware
  Serial.begin(9600);                                //set baud rate for the hardware serial port_0 to 9600
  myserial.begin(9600);                              //set baud rate for the software serial port to 9600
  inputstring.reserve(10);                            //set aside some bytes for receiving data from the PC
  sensorstring.reserve(30);                          //set aside some bytes for receiving data from Atlas Scientific product
}

void serialEvent() {                                  //if the hardware serial port_0 receives a char
  inputstring = Serial.readStringUntil(13);          //read the string until we see a
  input_string_complete = true;                      //set the flag used to tell if we have received a completed string from the PC
}

void loop() {                                        //here we go...

if (input_string_complete) {                        //if a string from the PC has been received in its entirety
    myserial.print(inputstring);                      //send that string to the Atlas Scientific product
    myserial.print('\r');                            //add a to the end of the string
    inputstring = "";                                //clear the string
    input_string_complete = false;                    //reset the flag used to tell if we have received a completed string from the PC
  }

if (myserial.available() > 0) {                    //if we see that the Atlas Scientific product has sent a character
    char inchar = (char)myserial.read();              //get the char we just received
    sensorstring += inchar;                          //add the char to the var called sensorstring
    if (inchar == '\r') {                            //if the incoming character is a
      sensor_string_complete = true;                  //set the flag
    }
  }

if (sensor_string_complete == true) {              //if a string from the Atlas Scientific product has been received in its entirety
    Serial.println(sensorstring);                    //send that string to the PC's serial monitor
    /*                                                //uncomment this section to see how to convert the pH reading from a string to a float
    if (isdigit(sensorstring[0])) {                  //if the first character in the string is a digit
      pH = sensorstring.toFloat();                    //convert the string to a floating point number so it can be evaluated by the Arduino
      if (pH >= 7.0) {                                //if the pH is greater than or equal to 7.0
        Serial.println("high");                      //print "high" this is demonstrating that the Arduino is evaluating the pH as a number and not as a string
      }
      if (pH <= 6.999) {                              //if the pH is less than or equal to 6.999
        Serial.println("low");                        //print "low" this is demonstrating that the Arduino is evaluating the pH as a number and not as a string
      }
    }
    */
    sensorstring = "";                                //clear the string
    sensor_string_complete = false;                  //reset the flag used to tell if we have received a completed string from the Atlas Scientific product
  }
}

I tried it, but it doesn´t work