TDS and ROs

[cjf12]

Trying to be sure my membranes are good. Spring water is 8ppm according to TDS. Yep. Only 8. After running through RO it measures 1ppm. I haven't washed yet and only ran 150ish gallons across 3 membranes that were stored. I feel like that's not enough variation to go off of. Thoughts.

Is there something I could add to water to see if they are working properly?

[carls47807]

You can add a pinch of salt to get the feedwater up to around 200. Then you should have less than 20 on the permeate side. Always check permeate with a sap hydrometer as well once the season gets started.