I use two dual inline TDS meters.
I have one on the waste out line so when I am flushing the system I can see the tds increase when i start the flush and when it comes back down to (in my case) about 40 it’s good to go and the other is after my di pod.
My second tds meter,,, I run dual membranes so I have both of the sensors after my membranes so I can see the condition of my membranes. Doing this gives you a good indication of weather your membranes need replacing or not.
Hope that makes sense
Sent from my iPhone using Tapatalk Pro