You can measure the concentration of salt water
It is a compact inline model of simple specification that allows continuous measurement of saline concentration. It is possible to output the Brix value for the recorder (DC 4 to 20 mA).
Low Cost & Simple
[Brine – DC4 to 20mA]
More Info:
https://www.atago.net/product/?l=en&f=products-cm-top.php#GDM48047