Extreme PH readings and temperature comp

[Brent]

NOTE: I HAVE UPDATED AND CORRECTED FROM THE ORIGINAL POST

I suspect there are a lot of guys out there with RO systems who, like me, do not have doctorates in chemistry.

This summer while trying to decide what new membranes to get I found the cleaning instructions on the DOW web site, and it was quite interesting. The difference between the effectivenesss of "soap" as the French Canadians call it, (sodium hydroxide) at difference levels of alkalinity was amazing. They recommend pushing the PH to 12. On a graph, the spread between 11 and 12 in effectiveness was huge. The change was pretty shallow up to 11, then went up dramatically.

So the question of getting something more accurate than a wide range color strip became obvious. Tonight I found some good reading on the omega.com web site
On this page click on the top left item. Of special note is the section in the pdf on temperature compensation. Because we should run the RO until the temperature reaches about 115 Deg F, and we're way out on the PH scale, the temperature compensation becomes important. (sounds like syrup density doesn't it) Anyway the document give you a chart that should be in the shack if you don't have a temperature compensated PH meter.

The document is Dow Form 609-23010-1010 and was written specifically for the FT30 RO membranes, and should apply to all their true RO membrances. It may not apply to the NF series of nano-filtration membranes

[Brent]

Please not the above post has been edited to make corrections and add the DOW document number for reference.

[danno]

Hi Brent -

I don't have the DOW cleaning instructions in front of me, but don't they recommend lowering the cleaing solution temp as you raise the PH. I recall that as you get up to 12 or 13 PH, you lower the temp of your solution.

[Brent]

You're correct Danno.

The document has a table for the different families of membranes.

Several members use NF 200-270 membranes and at
77 degrees the pH range is 1 to 12
95 degrees the pH range is 1 to 11
113 degrees the pH range is 3 to 10

For those using the XLE membranes (like me)
77 degrees 1 to 13
95 degrees 1 to 12
113 degrees 1 to 10.5

So my Airablo RO is pre-set to shut down at 120 degrees. Going to have to fix that or be very sharp late at night.

I am wondering if I start at say 77 degrees and pH 12 or 13, is the pH going to drop enough as the biofilm eats up some of the alkalinity as it gets washed off ? Hmmmm ?

More re-reading reveals if the pH of the alkaline cleaning decreases more than 0.5, then more caustic should be added. If you're doing an acid clean for minerals, and the pH goes up more than 0.5, then add more acid.

I have saved a couple of the Dow documents on our site.
Finding them on the Dow site is not easy, even when you use their own site search tool.
see the box at the very bottom of this page
http://www.duffyslanemaple.ca/syrup-equipment/syrup-equip.html

[danno]

More re-reading reveals if the pH of the alkaline cleaning decreases more than 0.5, then more caustic should be added. If you're doing an acid clean for minerals, and the pH goes up more than 0.5, then add more acid.

I have saved a couple of the Dow documents on our site.
Finding them on the Dow site is not easy, even when you use their own site search tool.
see the box at the very bottom of this page
http://www.duffyslanemaple.ca/syrup-equipment/syrup-equip.html[/QUOTE]

I also recall reading that if the solution turns a yellowish/greenish color after beginning the wash, dump it rather than adding more soap (if PH dropped) and start a new wash. Now, just waiting for my 1-14 PH strips. I had a heck of a time finding them, so wound up ordering them on-line.

[Brent]

Danno
I don't think strips are accurate enough. I'm going to get a meter. But the meter market is bewildering.

Everything from $18 to $1000 claims to be accurate to 0.1 at least. Most sell without reference solutions to re-calibrate. Some have to be kept wet all the time or soaked for 24 hours before they will read correctly. I quit at midnight last night trying to make sense of it all.

[sapman]

Please let us know when you think you find a decent meter! I got one last year. Seemed to work well for awhile. Then I figured I needed to cut the paper a little, which is nearly impossible, and never had correct readings again. Should have sent it back.

[Brent]

which one did you try Tim ?

I've seen instructions on some about cutting cloth.
I think to say these are finicky is an understatement.
They do not have a good reputation in the swimming pool crowd either.
Many of the more expensive ones have replaceable probes.
Maybe most folks buy the cheap ones that are made to be "sold"
and not to "work".

[Teuchtar]

I bought the Hanna hand-held meter two years ago. Also got the neutral and calibrating solutions. I also read that the elements fail after a year or two, but mine seems ok this year.
This year I'm putting a temperature monitor (auber instruments controller) onto my RO so I don't cook the membranes.
Much to learn, plenty to tinker with !

[sapman]

Not sure the make. It is red, maybe a Hanna, $30 price range.

[Brent]

In keeping with the basic idea that you get what you pay for I figure there has to be a reason that Hanna stays in business marketing more expensive models and hopefully
the $125 model I've picked will give more better results. It's on it's way. At the end of the season I'll try to remember to come back here and update the successes or failures of it. I picked the HI98130.