Hello, I wonder if Electrical Conductivity meter from DFRobot is designed to work permanently…
Sergi Barreda Lacambra

Hello Sergi. Dfrobot have said that the probe that comes with the EC meter is meant for use in a lab, not industry, and is not meant to be used permanently immersed in a liquid forever. That being said we’ve used it for months with no problems.
There is a range of EC probes, you need to get one with K = 1.0. We got one of the cheapest, E201WM, it’s ugly as hell and seems to work fine. They are about 20 quid on ebay. 
Are you putting together a hydroponic system?