advice about alkalininty and salifert test

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chrisseej

advice about alkalininty and salifert test

Post by chrisseej » Thu Oct 13, 2016 7:50 pm

hi excuse my ignorance but have been trying to get my head around water chemistry, I have bought a salifert test kit no problems with the test my tap water comes out at 49 ppm CaCo3 however when I tested my boiled water I get 87 ppm CaCo3!

I am I right in thinking there should be a decrease in alkalinity after boiling not an increase or am I totally on the wrong track

would appreciate some advice


Cheers

BenB

Re: advice about alkalininty and salifert test

Post by BenB » Thu Oct 13, 2016 8:04 pm

You sure you doing the test right? It should certainly reduce! You measuring the amount of reagent you're using rather than left in the syringe? :wink:

chrisseej

Re: advice about alkalininty and salifert test

Post by chrisseej » Thu Oct 13, 2016 8:42 pm

you could be right about that, I may have read the instructions wrong. if I do it the other way round I get un boiled 234 ppm and boiled 182 ppm, this does make more sense.

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Re: advice about alkalininty and salifert test

Post by Eric » Thu Oct 13, 2016 9:10 pm

chrisseej wrote:you could be right about that, I may have read the instructions wrong. if I do it the other way round I get un boiled 234 ppm and boiled 182 ppm, this does make more sense.

The indicator is blue/green when pH is greater than 4.5 and pink when pH is less. the reagent is a mild acid which neutralises alkalinity, the more used to achieve a colour change the more alkalinity the water contains. Alkalinity in excess causes serious problems in brewing, but can with suitable acids be perfectly controlled at little cost and effort.
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Re: advice about alkalininty and salifert test

Post by Kev888 » Thu Oct 13, 2016 9:26 pm

BenB wrote:You sure you doing the test right? It should certainly reduce! You measuring the amount of reagent you're using rather than left in the syringe? :wink:
Yep, the manufacturer's instructions are to use the syringe reading, i.e. 'what is still left in the syringe' just as the colour begins to show signs of changing. No maths required.

In the kits I've had there has been a check solution, to allow you to check that your readings match. Someone recently said theirs did not have this, I don't know if that was an error at packing or if the kits no longer include it.
Kev

chrisseej

Re: advice about alkalininty and salifert test

Post by chrisseej » Fri Oct 14, 2016 10:22 am

Thanks for all the advice it makes sense that the alkalinity is measured by the amount of reagent used but am still I bit confused by the instructions which read

"Hold the syringe with the tip facing upward and read the position of the now upper end of the black piston, the syringe has graduations 0.01ml, read the kh alkalinity value from the table"

It dosent tell you what to read specifically if it's the amount used or amount left in syringe, it would make sense to use the amount used.

Also on the instructions it says "a free reference check kit is sometimes included"

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beerfishchris

Re: advice about alkalininty and salifert test

Post by beerfishchris » Fri Oct 14, 2016 10:54 am

The Reference vial is a relatively new thing I sell these in my aquatic shop have done for years, there may be in date stock that is still around that doesn't have it but all new stock should come with it.

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Re: advice about alkalininty and salifert test

Post by Kev888 » Fri Oct 14, 2016 11:18 am

chrisseej wrote: It dosent tell you what to read specifically if it's the amount used or amount left in syringe, it would make sense to use the amount used
As mentioned before, it is the amount left in the syringe. The manufacturers instructions say to 'read the position of the.. black part of the piston' and the column on the left of their table is similarly headed 'reading', i.e. the syringe reading. The syringe does not read what has been used, it reads what is left, and that is what you should use.

The table is clever enough to save you doing any maths (assuming you start the syringe at exactly 1.00ml as instructed). If you find yourself using a calculated value (to determine what has been used) then this is not a reading and is not correct.

It is simply the syringe reading you need to use
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Re: advice about alkalininty and salifert test

Post by Kev888 » Fri Oct 14, 2016 11:32 am

beerfishchris wrote:The Reference vial is a relatively new thing I sell these in my aquatic shop have done for years, there may be in date stock that is still around that doesn't have it but all new stock should come with it.
This is the second time recently that I've heard of kits not having the check solution, but I've been buying them for several years and even the earliest ones have had it. I wonder if there may be two versions or if the newer ones are phasing it out or something.

They did change the strength of things some years ago, so its important to use the table supplied with the kit to convert ml to a meaningful value. Somewhere on here someone had posted a table from an older kit, and that may no longer work.
Kev

chrisseej

Re: advice about alkalininty and salifert test

Post by chrisseej » Fri Oct 14, 2016 1:07 pm

Cheers for the advice the only problem is when I compare tap vs boiled alkalinity tap water comes out as kh 2.2 with 0.84 ml left in Syringe whilst boiled comes out as 3.8 kh with 0.74 left mI. Syringe. This dosent seem to make sense as alkalinity should decrease post boil. If I do it for reagent used alkalinity goes down
So something Is not right previous post says that it is the amount of reagent used as its a mild acid

Conclusion - still confused

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Re: advice about alkalininty and salifert test

Post by Kev888 » Fri Oct 14, 2016 1:41 pm

Those KH values are correct for the syringe readings, so we can now rule out that as a cause.

As to why your alkalinity results rose I don't know, it could be due to evaporation or there could be some other error in the measurement process. It is a great pity your kit lacks the check solution, as that would let you double-check your understanding of how to carry out the test. But even if you understand it correctly, its still possible to make mistakes - is it possible that you used 5ml of water by mistake (rather than 4ml) or tested the boiled sample whilst still hot?
Last edited by Kev888 on Fri Oct 14, 2016 5:09 pm, edited 1 time in total.
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Re: advice about alkalininty and salifert test

Post by Sadfield » Fri Oct 14, 2016 2:03 pm

Just a thought, could beerstone (if it was there) or any cleaning contaminate cause this anomaly?

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chrisseej

Re: advice about alkalininty and salifert test

Post by chrisseej » Fri Oct 14, 2016 3:04 pm

I really dont understand this, I have done the test numerous times on boiled and un boiled water always hitting the same numbers so there is some realibilty in the results.

I have just retested all at room temp 8.4 ml left in Syringe for Unboiled and 7.4 ml left in syringe for boiled.

As a control I tested Evian water which on label says hco3 - at 360 indicating pretty hard water when tested this required 1.2 ml of reagent to change colour which is off the chart supplied with the kit.

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Re: advice about alkalininty and salifert test

Post by Dave S » Fri Oct 14, 2016 3:07 pm

chrisseej wrote:I really dont understand this, I have done the test numerous times on boiled and un boiled water always hitting the same numbers so there is some realibilty in the results.

I have just retested all at room temp 8.4 ml left in Syringe for Unboiled and 7.4 ml left in syringe for boiled.

As a control I tested Evian water which on label says hco3 - at 360 indicating pretty hard water when tested this required 1.2 ml of reagent to change colour which is off the chart supplied with the kit.
What syringe are you using? The one that comes with the kit only holds 1mL
Best wishes

Dave

chrisseej

Re: advice about alkalininty and salifert test

Post by chrisseej » Fri Oct 14, 2016 3:21 pm

I use the supplied, I had to refill and got a colour change after adding an extra 0.2 ml also just tested boiled Evian lots of scale left in pan got a colour Chang after adding 9.5 ml so 0.5 left in syringe

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