If the RO was running correctly and the membrane(s) are in good condition the permeate should be at or very near 0.0 sugar. I suspect the membrane(s) need replacing but it could be another issue. Could be a bad seal too, allowing some concentrate to leak into the permeate side, but the membrane(s) are most likely the issue.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.