Salifert vs Water Report

(That's water to the rest of us!) Beer is about 95% water, so if you want to discuss water treatment, filtering etc this is the place to do it!
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MarkA
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Salifert vs Water Report

Post by MarkA » Thu Oct 12, 2017 3:13 pm

Hi,

I've now got a water report from Wallybrew and it gives a figure for alkalinity of 39 CaC03.

I took a Salifert test on the same water as I bottled it which gave me a figure of 28 CaC03.

I did the 4ml water/4 drop test and the syringe reading was 0.88 which gives the meq/l figure of 0.56 (then x 50 = 28)

Am I missing something here or making the wrong calculations?

Please help!

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Eric
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Re: Salifert vs Water Report

Post by Eric » Thu Oct 12, 2017 5:23 pm

A Salifert kit is usually reliable, as are analyses by Wallybrew. Did you keep the test sample? I suspect it might have been on the cusp and after a little while might return to blue.
I note the reading when the indicator turns pink, but continue adding reagent and if it turns a stronger pink use that figure until the colour does not change.
Your calculation is indeed correct.
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Re: Salifert vs Water Report

Post by MTW » Thu Oct 12, 2017 6:42 pm

I wanted to know how accurate the Salifert was too and also tested my Wallybrew sample. It was within a couple of points if memory serves, around 120. They seem pretty reliable generally.
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MarkA
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Re: Salifert vs Water Report

Post by MarkA » Thu Oct 12, 2017 6:43 pm

Thanks Eric. Unfortunately I didn't keep the test sample. I took the reading when it had turned pink with the first drop after the blue colour and it appeared stable. I'll leave it longer next time to see if it returns to blue.

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vacant
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Re: Salifert vs Water Report

Post by vacant » Thu Oct 12, 2017 8:40 pm

That difference looks significant (approx 30 vs approx 40) Could it be explained by three drops of reagent rather than four?
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MarkA
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Re: Salifert vs Water Report

Post by MarkA » Thu Oct 12, 2017 9:13 pm

vacant wrote:
Thu Oct 12, 2017 8:40 pm
That difference looks significant (approx 30 vs approx 40) Could it be explained by three drops of reagent rather than four?
99.9% sure it was 4 drops (always room for doubt though!)

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Kev888
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Re: Salifert vs Water Report

Post by Kev888 » Fri Oct 13, 2017 10:00 pm

As Eric says, both Wallybrew and the salifert kit are reliable. If it was not the exact same sample tested then the water could have varied, mine ranges between 0.67 and 2.05 meq routinely.

Also there is scope for some user interpretation error from the kit (as well as miscounting drops etc), or I suppose the kit may have become contaminated in some way. A classic mistake for me is to use the full 5ml range of the water syringe, instead of the 4ml specified. The kits previously came with a check sample to verify things were working, but apparently some (all?) recent ones no longer do.

Also, make sure you are using the look-up table that came with the kit. (IIRC there is one reproduced on this forum somewhere which has been incorrect for several years). The syringe reading to meaningful units (kh or meq) is a manufacturer-specific conversion, and subject to change.
Kev

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MarkA
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Re: Salifert vs Water Report

Post by MarkA » Sat Oct 14, 2017 4:22 pm

Kev888 wrote:
Fri Oct 13, 2017 10:00 pm
Also there is scope for some user interpretation error from the kit
I was waiting for the liquid to turn pink but have just re-tested and taken a reading at the point before (where it turns a grey/purple colour) and it has given me a figure of 39.5 CaC03 so I will use this as a reference point for the future.
Kev888 wrote:
Fri Oct 13, 2017 10:00 pm
but apparently some (all?) recent ones no longer do
My kit's instructions read "A free reference/check solution is sometimes included" Unfortunately, not in mine!

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Re: Salifert vs Water Report

Post by Kev888 » Sat Oct 14, 2017 9:56 pm

Ah, that seems consistent with WB's result then, so I think we can have reasonable confidence in around 39ppm being the correct value.

It used to be felt by some fairly informed people that the point at which the kit started to turn colour could be more accurate than the point when it had fully done so. But at least for me the difference is very slight, maybe one line lower in the lookup table, so IMO seems unlikely to have been the main cause of the previous rather larger discrepancy.
Kev

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