New to me r/o

[Atgreene]

I intended to build a small r/o, but had a chance to buy a Water guy. I don't have any complaints with the unit, but I have no experience to base my issues against. I bought new MES membranes (Clay is a great resource), but I'm showing .25% +- in my permeate? Am I not cleaning the membranes enough, bad o ring, or am I missing something? Running good clean sap, 3-4% from the trees. Should I boil some permeate to test the accuracy of my reading? Refractometer has been calibrated on distilled water off the steam hood. I've tried different pressures, doesn't seem to matter. First day i ran the new membranes, had a little in the permeate, .2 or so. Wrote it off as operator error. The other night ran 450 gallons, permeate was zero, today running 600 gallons its hovering around .25.

On edit, pressure doesn't seem to make any difference, tried 190 up to 230 psi, no change.
Hydrometer shows 0.

Any suggestions or thoughts?

[GeneralStark]

You really need to boil the permeate to more accurately test if the membranes are passing sugar. Take a gallon and boil it to 4 oz. or so and then test with the refractometer.

[Atgreene]

I boiled a small amount with no sugar found, I'm going to run another larger test to be sure. I'm beginning to suspect something else is throwing my refractometer off. Everything I've tried proves no sugar. Has anyone ever seen false readings on a refractometer?

[bowhunter]

Yes. You can't trust the refractometer down in that range. If the refractometer isn't completely clean you will have traces of sugar on it from testing sap and concentrate, etc. I think you will also see some zero drift. If you boiled the permeate and you didn't find any sugar, you don't have any leak through. If you do have leak through it's more likely the o-rings than the membrane.

[Russell Lampron]

You can't calibrate a refractometer accurately with water off of the steam hood. There are still some traces of sugar in it that escape the boiling sap in the steam. Buy some distilled water and calibrate with that.

[Atgreene]

I've boiled some permeate and got nothing. Its odd that the refrac shows nothing on the distilled water draining off the hood, yet picks up on something in the permeate. Something to keep in mind if you have an ro, it can happen.