RO water ppm rising

I've noticed that if I fill my kettle with RO water and let it sit for a day or two with the lid on, it reads over 100ppm.

RO water stored in glass jugs reads 10-15ppm.

Is the water in my kettle picking up all that extra stuff from the air? My cleaning process for the kettle is pretty thorough, but maybe I'm missing a spot or two and that's dissolving solids into the water?

Yes, you will get changes in RO water exposed to air.

Maybe a better question would be if that's a typical increase for air exposure in a kettle sitting for 1-2 days with the lid on? I know the lid isn't going to provide a perfect seal, but that seems like a lot to me.

Carbon dioxide from the air dissolves in water that doesn't contain any but I am skeptical that it would be enough to exhibit conductivity of 100 mg/L NaCl equivalent. I'll go for residue on the pot until I can access the reference stuff I need to calculate the conductivity at CO2 equilibrium.

I'm pretty thorough with my cleaning. I rinse and scrub with water, then soak with warm water and PBW, scrub, then rinse several times with water, then soak with Star San, then rinse several more times with tap water. I only have tri clover fittings on my kettle, no threads, though admittedly I haven't taken those apart to clean yet. Maybe there's some gunk in there I'm not seeing that is contributing to the ppm rise.

Isn't RO water corrosive to metals?

Yes it is but only very weakly so that a metal pipe conveying RO water will develop a pinhole leak after several months but not to the extent that 10's of mg of aluminum will dissolve in a day or 2. At least I don't think so.

Water in equilibrium with the air contains 0.13 mg/L bicarbonate ion and has conductivity of about 1 uS/cm. This would measure about 0.8 ppm completely masked by the ions the RO membrane didn't catch. A conductivity reading of 100 ppm means the equivalent of 100 mg of NaCl has dissolved in each liter of the water. That's quite a bit of stuff. Aluminum bicarbonate? I've my doubts but a simple experiment would tell. Grab a piece of scrap aluminum and prepare some powder with a file. Put this in a glass dish and cover with RO water. Leave open to the air. If the conductivity climbs to near 100 ppm over the course of a couple of days aluminum bicarbonate it is.

Now with respect to cleaning: 100 ppm would be a lot of material from imperfect cleaning. Five gallons (20L) at 100 ppm implies 2 grams of dissolved material left behind after cleaning. That's surely more than can hide in threads and crevices. This is mysterious for sure.

That is pretty mysterious. I collect water a day in advance and take a TDS reading on brew day to make sure I don't add minerals twice by mistake. If there is a rise it's not something I notice. Still reads 5-6. After additions I do a gut check to make sure I'm in the 100 ballpark and not 5 or 300.

I don't know why I assumed the kettle is aluminum. It doesn't say that anywhere here. If the kettle is stainless then this is even more mysterious.

It's a stainless steel kettle. I smells pretty metallic when I poke my head in there, which is a little strange as I haven't experienced that with other stainless steel stuff.

About the best I can suggest at this point is to pack up a liter of the stuff and send it off to Ward Labs.

ajdelange said:

About the best I can suggest at this point is to pack up a liter of the stuff and send it off to Ward Labs.

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Should I order the brewer's test if I were to do that?

Go for the test that gives you the most ions reported within the limits of what you want to spend. But before you do that be sure to check your meter.

My meter is reading 6ppm straight out of the filter, so I do think it's accurate. I've also calibrated it.

I took apart all the fittings in the kettle and cleaned them, though I didn't find anything in there. Gave the kettle a good scrub with soap and water, rinsed several times, did a PBW and warm water soak, then sprayed it down with the hose multiple times. I think it's spotless. I'm filling it with RO water again, and will let it sit for a couple of days to see if the TDS goes way up again. If it does, I'll collect a sample to send off to Ward Labs. If it doesn't I know it was some residue in the kettle. It's currently been filling for about 90 minutes, and the water in the kettle is at 3ppm.

Epos7 said:

My meter is reading 6ppm straight out of the filter, so I do think it's accurate. I've also calibrated it.

I took apart all the fittings in the kettle and cleaned them, though I didn't find anything in there. Gave the kettle a good scrub with soap and water, rinsed several times, did a PBW and warm water soak, then sprayed it down with the hose multiple times. I think it's spotless.

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Did you do the final rinsing with RO water? If not, I suspect this is your answer.

Russ

Can you fill a different container with the same water - perhaps a glass jar? Let it sit in the jar for the same amount of time and see what your meter reads in the end. Maybe do two jars - one sealed and one not.

If the kettle measurement still drifts up and the jars don't, then you know it's the kettle (but not what in the kettle).

If it's a 20L kettle and he left 1 L of rinse water behind (and of course it wouldn't be anything near that much) the rinse water would have to be at 2000 ppm in order for a mix of the rinse water with 19 L of RO water to be at 100 ppm so I don't think that is his answer. But I do think a final rinse with RO is a good idea.

PlinyTheMiddleAged said:

Can you fill a different container with the same water - perhaps a glass jar? Let it sit in the jar for the same amount of time and see what your meter reads in the end. Maybe do two jars - one sealed and one not.

If the kettle measurement still drifts up and the jars don't, then you know it's the kettle (but not what in the kettle).

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I have some glass jugs I store RO water in, sometimes for up to a week. It stays at 10-15ppm in the glass jugs, so it's definitely confined to the kettle.

I filled the clean kettle with RO water a little less than two days ago. When I first filled it, the water read 3ppm. Now it reads 320ppm. It's got to be leaching something out of the kettle.

0 to 320 ppm is one heck of a change! Is the 320 higher than the feedwater you're sending to the RO?

Well, 3 to 320 ppm, but yeah it is!

I've been having a lot of efficiency problems. I don't know if it's possible for ions leaching into my brewing water to disrupt the starch conversion process, but it's the best guess I've got at the moment.

Buckeye_Hydro said:

Is the 320 higher than the feedwater you're sending to the RO?

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Yeah, the tap water is sitting at 55ppm.

Maybe you should acid passivate your pot?

I used this as a reference:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110001362.pdf

I used citric acid in a 5% concentration wixed in RO water, held at 140f for an hour in my kettle filled to the brim. It definitely worked in removing the free iron on the surface, the water afterward had a noticeable iron/metallic scent to it.

Epos7 said:

I filled the clean kettle with RO water a little less than two days ago. When I first filled it, the water read 3ppm. Now it reads 320ppm. It's got to be leaching something out of the kettle.

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Whatever it is there is a whole lot of it. If you are filling with 10 L that's 3 grams of this mystery substance.

Well I will send some off to be tested and hopefully figure out what it is!

The_Bishop said:

Maybe you should acid passivate your pot?

I used this as a reference:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110001362.pdf

I used citric acid in a 5% concentration wixed in RO water, held at 140f for an hour in my kettle filled to the brim. It definitely worked in removing the free iron on the surface, the water afterward had a noticeable iron/metallic scent to it.

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Something worth looking into, thanks! Maybe I'll conduct the same experiment afterwards and see if it made a difference.

If it is iron, that could explain my poor conversion efficiency:

http://www.mbaa.com/meetings/distri...ingPresentationBrewingRawMaterialsQuality.pdf

Iron levels should be low to avoid incomplete saccharification

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Well this is embarrassing - the high (320ppm) reading I measured may have been the result of instrumentation error.

I've continued taking readings on the RO water stored in the kettle. I have been able to reproduce the high reading with a measurement 30 minutes ago of 380ppm, but I'm also getting some readings in the 5-10ppm range, which is what I would expect from RO water.

My procedure is to clean the instrument with distilled water, rinse the sensor and sample cup with the water to be measured, take a sample, agitate the sample, and take a reading, allowing 10-20 seconds for the meter to stabilize. This is how I arrived at 320ppm, which I was able to repeat with a second measurement. However, today after I measured 380ppm, I measured some tap water (60ppm) and went back to the RO water, at which point my meter read 8ppm. I repeated the measurement of the RO water, and was still in the 5-10ppm range.

At this point I think it's more likely the RO water in my kettle is sitting around 5-10ppm, and the 300+ ppm readings I have measured are the result of some instrumentation error. Strangely, I get consistent results from tap water and RO water stored in glass jugs. The RO water stored in the kettle seems to throw a high reading at times. I'll try re-calibrating my meter and continue testing.

What meter are you using?

It's a Hach Pocket Pro+ Multi2. Basically the pH meter that is very popular around here with added conductivity functionality.

Good meter. Just wanted to make sure you weren't using one of those $8.99 "ebay special" TDS meters.