Lessons from my pH meter

[Brent]

So I got the XLE-4040s and downlaoded DOW's instructions for cleaning and it is pretty obvious from the charts they provide that the best cleaning, in fact almost all of it, happens when you get right up to pH-11 and temps up near 115 degrees.

So cleaning started today. I did a rinse of about 150 gallons. Then filled the wash tank 1/2 full and added a tablespoon of Sani-Osmo from Ariablo and started the pumps. The pH shot up to high so I quickly drained off and refilled until I got the pH to just under 11. Then I let it rip until it shut off at the hi temp limit. I decided to re-check the pH .... It was down to 10.25. Hmmm.... added a quart tablespoon and fired it up again. Ten minutes later the pH was up to 10.8.
So I added another quarter tablespoon and let it go 10 minutes more .... same thing ... the pH was 10.78
Repeat the process about 6 more times add a quarter tablespoon, run the temp up

I'm still going at it but it seems like simply making the correct solution and going 1 cycle does not get you where you want to go. As you approach the active temperature the alkalinity gets consumed in the cleaning, so you need to keep adding when it drops down. I did see this in the DOW literature somewhere, that is to keep checking and adjusting the pH as you go.

I guess there's a big difference between doing a cleaning cycle and really cleaning the membranes. I'll update this when I finally get to the and the pH stays stable.

[Brent]

It took about a dozen cycles of adding 1/4 tablespoon before the drift down sort of stabilized. So I ended up with almost 3 X the wash powder going in that initially sent the pH over the suggested limit.

Now I'm debating whether the one season on the new membranes is enough to justify an acid bath for the minerals.

[Brent]

So I decided to do the acid clean too.

No surprise that when I added enough to show 3.4 on the meter, a half our later it was up to 4.5.

Now I've done that 3 times and still going.

[RO_Guy]

So I decided to do the acid clean too.

No surprise that when I added enough to show 3.4 on the meter, a half our later it was up to 4.5.

Now I've done that 3 times and still going.
How did your muriatic acid wash go? Was there a noticeable improvement in your membrane efficiency?

[Brent]

I only used citric acid ... the recommended acid from Airablo for the PVD-1 membranes. DOW literature for the
XLE-4040s ranks the citric acid as not so effective compared to the muriatic acid. The membranes were performing virtually as new when I shut down so there really wasn't a big need for the cleaning ... so I didn't bother with a performance test after cleaning.

[Jeff E]

Does your PH meter correct for temp changes?
If not you may be chasing a false reading.
I watch my correcting meter change as the temp measuring side gets up to temp. Lets say the wash is actually at 12 deg C, and when I put the meter in it is at 8 deg. Say it reads PH 9.8, then as the temp meter goes up the PH goes up as well. With a 4 deg temp change the PH may change by 1-2.

With the CDL we wash after every use. Only with the soap. I had not heard of an acid wash...

[Brent]

After hearing lots of tales about unreliable meters and finding those complaining bought $25 cheapies, I put out
$ 150 for mine and it does the temp corrections automatically ... and it does swing through a lot of numbers as it does the temp comp. My thinking is the has to be a reason an instrument maker has $ 150 and $ 200 models or they wouldn't sell enough of them to justify having them. So the folks out there in trades that need good numbers must buy them. Amateurs like us need to take note.

I recalibrated right before I started the wash cycles and cross checked with strips, which really are not good enough when your trying to hit the difference between 10 and 11.