Before spending money
new membranes, I would suggest doing the following.
1. Check if the permeate conductivity alarm
is timed on the control panel and increase the time before shut down, or increase the number to 900 temporarily. Membranes "wash down" and it takes time for them to reach the set number and it could be that the system is simply not allowing enough time for this process.
2. The conductivity probe (salinity) will not read properly if installed incorrectly. It should be installed so that the permeate (product) water runs into it using a T connection and not hooked into a water line where the water just passes over it. Air, or not being totally submerged into the water can effect the reading. Considering that you say it is installed incorrectly, I'd try this first.
3. Do buy a hand held conductivity meter as Tellie suggested to check everything (they are cheap) or you can also buy a bottle of "conductivity standard solution" to test that your conductivity monitor
is operating correctly or if calibration is needed. Possibly a probe replacement. For a quick check, but a bottle of water, pull the probe and stick it into the bottle to see what it reads. If under 100, it's probably reading correctly.
4. you can also bypass the conductivity alarm
inside of the panel if you find the probe bad or even if you wish or need to make water by tracing the conductivity wires in the panel and either jumping the probe connections with a small jumper wire, or disconnecting one of the conductivity wires. this will depend if they are connected using a N/O or N/C connection.
Hope this helps helps.