Would a line like this work with the serial library:
val_pH = Serial.read(26.5) ???
No. The Serial.read() function does not take any arguments. It simply reads whatever is on the serial port.
You send the device commands, like "read(someTemp)" using Serial.print() assuming that you have the device connected to the serial port pins. It responds with character data that you read using Serial.read(), one character at a time.
They seem to work as RS232 using low voltage so no need for any interfacing with an Arduino UART ports.
A serial device without the need to use the serial port. How's that working for you?