I always add permeate, clean sap, almost syrup or distilled water. You could also add water if it is rather soft but not softened. Bottled spring water is another option.
Yesterday when I tested a batch being put into a barrel, I actually had to mix 2 whole gal. of permeate and blend it in well before putting it in the 26.5 gal barrel. Must be the barometric pressure changed and I failed to recheck, making the auto draw open at a too dense temperature. I'll check more often to minimize that. It doesn't hurt anything but it just takes time to adjust the density.
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.