pH of RO Water

[chrisb8]

I am sure that when I first got my RO filter I tested the output water and it was pH 6 (cheap pH meter). I have recently tried to be a bit more scientifically accurate with my water treatment and have invested in a more expensive HM pH meter. Tested my RO water yesterday and it was 4.9. Checked calibration of meter etc and all correct. I understand that RO water can have a lower pH as it absorbs CO2 from the atmosphere but I was still surprised by the result from water collected in the past half hour. Do people generally test their RO water pH before brewing? I'm thinking of what figure to enter into the brewfather water calculator... Thanks.

 

[The-Engineer-That-Brews]

That certainly sounds lower than I would expect

 

[chrisb8]

That certainly sounds lower than I would expect

That's what I was thinking

 

[Hazelwood Brewery]

I test mine every time. If I test the water shortly after collecting it as you have done it’s usually around 6.5

Edit: just checked my records. Today was 6.51, last time it was 6.57

 

[Hazelwood Brewery]

What’s your TDS reading?

 

[chrisb8]

What’s your TDS reading?

TDS was 360 from the tap water and 6 from the RO filter

 

[Hazelwood Brewery]

TDS was 360 from the tap water and 6 from the RO filter

It sounds like you need to change the ionisation crystals, are they an orangey colour?

 

[The Baron]

I am no expert but out of interest have just been reading on the internet some say the PH should be between 5 and 7 but some say it should 7 which is neutral?.
I would say that yours is erring on the edge of what is expected but it would be brilliant for doing a sour beer.
By the way with it being low and if I am correct doesn't the grain when added lower the PH more?
Have you been brewing with this water as low before and have you noticed a tartness to your beers just out of curiosity

 

[The-Engineer-That-Brews]

What reading does that pH meter give for your tap water?

 

[Hazelwood Brewery]

I am no expert but out of interest have just been reading on the internet some say the PH should be between 5 and 7 but some say it should 7 which is neutral?.
I would say that yours is erring on the edge of what is expected but it would be brilliant for doing a sour beer.
By the way with it being low and if I am correct doesn't the grain when added lower the PH more?
Have you been brewing with this water as low before and have you noticed a tartness to your beers just out of curiosity

RO water has no buffering capability, one drip of something alkaline will turn the water alkaline. Also heating the water will drive off the CO2 and the pH will rise.

Water pH doesn’t really give any indication of mash pH.

 

[The Baron]

RO water has no buffering capability, one drip of something alkaline will turn the water alkaline. Also heating the water will drive off the CO2 and the pH will rise.

Water pH doesn’t really give any indication of mash pH.

Told you I wasn't a expert

 

[chrisb8]

What reading does that pH meter give for your tap water?

Tap water was 7.5

 

[chrisb8]

It sounds like you need to change the ionisation crystals, are they an orangey colour?

They were but I changed them before this test. Bought this MB-115 Mixed Bed DI Resin for Water Fed Pole Window Cleaning and Reverse Osmosis. The crystals I have been sent are orange already - I guess the slightly cheaper price over the other option on their site was because they were not colour change ones Or have I bought the wrong type??

 

[The-Engineer-That-Brews]

Tap water was 7.5

Hmmmm I'm not a chemist, but can't think of anything in the RO process that could possibly take the water from 7.5 down to 4.9. No way.

Sorry if I'm "teaching my Grandmother", but did you remember to flush the membrane out well before use with the bypass valve open...? (the membrane comes packaged with liquid in it that keeps it 'fresh' and it definitely isn't pH neutral)

 

[chrisb8]

Hmmmm I'm not a chemist, but can't think of anything in the RO process that could possibly take the water from 7.5 down to 4.9. No way.

Did you remember to flush the membrane out well before use with the bypass valve open...?

I was a bit eager to test my pump so flushed for about 2 minutes instead of my usual 10

 

[The-Engineer-That-Brews]

I was a bit eager to test my pump so flushed for about 2 minutes instead of my usual 10

2 mins might be a bit marginal but I doubt it would have had the effect you've seen.
I'm wondering about those DI granules... I too use the 'window washing' ones - but with a DI stage you really should be getting 0 TDS. I wonder if they needed rinsing through...
Is it possible you could test the pH of the RO water before it goes through your DI stage?

 

[chrisb8]

2 mins might be a bit marginal but I doubt it would have had the effect you've seen.
I'm wondering about those DI granules... I too use the 'window washing' ones - but with a DI stage you really should be getting 0 TDS. I wonder if they needed rinsing through...
Is it possible you could test the pH of the RO water before it goes through your DI stage?

It's certainly something I could try. Probably won't be until next weekend now though...

 

[chrisb8]

2 mins might be a bit marginal but I doubt it would have had the effect you've seen.
I'm wondering about those DI granules... I too use the 'window washing' ones - but with a DI stage you really should be getting 0 TDS. I wonder if they needed rinsing through...
Is it possible you could test the pH of the RO water before it goes through your DI stage?

I was also hoping for a lower TDS, especially looking at the results posted by @Hazelwood Brewery previously. Perhaps I need a new membrane? I have only had it since January and only produced perhaps 250L of RO water though

 

[The-Engineer-That-Brews]

I doubt very much that your TDS could be due to poor performance of the membrane - the DI granules on their own should take even straight tap water down to zero TDS. In fact that's what I used to do when I only needed small quantities of de-ionised water (it's just that the DI granules wear out really fast if you do that).
Your setup hasn't got one of those final filter stages that puts 'flavour' back into the water has it?

 

[The-Engineer-That-Brews]

Mind you, my DI vessel is quite large... (and no, I don't still use it without an RO filter )