Hardware to use to measure ph

Hi. I am looking at controlling the ph level of water in a small tank for a project. What is the best hardware option for me with using an arduino. I want to measure the ph and when it reaches 4 for example i want to open a valve with a digital out signal. Also i need to be able to connect the arduino to lab view.

Thank you

Search for "arduino ph probes".

Your only option for connecting to Labview is the serial port.