pH of Permeate (in preparation of an acid wash)

[fireant911]

I am attempting my first ever acid wash on my RO. According to the information on the Mattatuck Madness site, a pH of 2 to 3 is the target. I added only a small about of citric acid to the permeate and saw a pH level of about 1.5 (I added approximately half the 1/4 cup). I have a pH meter but I am questioning the reading that I am getting... I diluted and diluted and diluted which makes me question the reading I am getting. What is the pH level that others are seeing in their raw, untreated permeate?

[Bricklayer]

6-8 is normal ph for raw permeate.
I think you will be ok with a reading of 1.5. It will go up when you circulate it through the membrane because there is still permeate in the membrane and system. So it will water it down a bit. I usually have to add a little citric once I circulate it through the RO for a couple minutes.
I just use ph strips with a range of 0-14.
I originally had a digital ph meter. But always questioned it.
Usually I only test the raw permeate when I’m doing a rinse. When it stays at 6-8 Whatever colour that is I forget. Think it’s yellow. I know the membrane is clean or at least Dosnt have any acid or soap left in it.

[fireant911]

Thanks Bricklayer! I recalibrated my pH meter with the powder that came with it and retested the raw, untreated permeate which agreed with your numbers; however, the pH of the solution in the system was reading 0.00. I ended up dumping most of the permeate I was used as the pH was still crazy low. Without any other solution to address this, I added a little baking soda and that, along with the treated permeate already in the system, allowed the pH to finally come up to 2.4. I hope that the addition of baking soda is acceptable in this situation??? I recirculated this and continued monitoring the pH and it remained steady.

Since this is my first season of using the Reverse Osmosis (and only my second season of making syrup), I am not comfortable nor at ease with the dedicated cleaning procedures for these systems. I have made notes in my maple notebook so that I do not repeat this mistake next season.

[Bricklayer]

I am pretty sure baking soda would not be a good thing to be putting in your RO. Never heard of anyone circulating permeate with baking soda.
I’m not a big fan of the digital ph meters.
Usually the soap you buy especially for RO’s is buffered. Meaning it won’t go over 12 ph.
I know the stuff I use from CDL is. So I just mix a big cup in. And then stir it and check it. If the strip turns purple it’s good.
Not exact. But I’m in the ballpark.
With the acid I do the same thing. But only add half. Like a half cup. Stir it. Then check it. Add a little more then check it again. When it turns whatever colour is ph2 or close to it I start circulating.
It’s not an exact science. And the ph levels they tell you that the membranes can withstand are Probley inflated a little for safety. If your just circulating it for an hour or two and you are 1 or 0.5 ph over or under I don’t think it is gonna cause any damage.

[DrTimPerkins]

Chemistry of permeate can be found at: https://mapleresearch.org/pub/compositionofsap-2/

Not sure how the RO will deal with baking soda that hasn't dissolved well.

pH strips tend to be far easier to use in practice than pH meters. No batteries needed. :)

[fireant911]

Chemistry of permeate can be found at: https://mapleresearch.org/pub/compositionofsap-2/...

Dr Perkins,
Great article! I have saved this for future reference as it answers questions that I have not even asked yet!!! I saw another article of yours while looking, "Antimicrobial Silver in Maple Sap Collection", that I found interesting as well - I had been wondering about this very thing. The two articles addressing "Why are my tapholes leaking, and what can I do about it" was also VERY informative and applicable (as I have been contemplating this very issue as well).