Hi, I bought this for my work and its working good. I want to know about JST pin you have provided me with, Could you share details about Jst pin I cant find any like it.

Sure. It's:
JST PH2.0 4pin
You could easily get this kind of connector in your local shop.

This sensor is not waterproof, so it could not detect seawater.

We think this sensor could not detect the PPB concentrations, the resolution for this sensor is 1PPM according to the wikipage.