Alkalinity: Salifert vs. Murphys

[OvenHiker]

I recently received results of a liquor analysis back from Murphys and was surprised at how high they measured the alkalinity. I have an ageing Salifert kit which I've just used to check the very same sample that I sent to Murphys. The Salifert kit measured it 228.5 ppm of CaCO3, against Murphys 285 ppm of CaCO3. That's quite a big difference, so I'm wondering whether anyone knows whether this is due to my ageing Salifert kit. Which direction does the error go when the kit starts to get old?

Ironically, the anion/cation balance is better when I use the Salifert result. Go figure!

[WallyBrew]

You do not have a sodium or potassium figure so calculating your alkalinity is not possible.

However, using the figures supplied the alkalinity calculates as 178 as calcium carbonate.

Chloride is usually combined with sodium and potassium. Disregarding potassium you need 0.666meq of sodium to balance the chloride. This would be equivalent to 15.3mg of sodium per litre. Entering this figure into the calculation gives an alkalinity of 212 as calcium carbonate.

I'll leave the rest to your imagination.

[OvenHiker]

Cheers for that, WB!

Sodium in my tap water has been about 10 to 11 ppm in every water report, if that helps?

I appreciate that home kits are not going to give very accurate results. But going by the Murphys figure, the home kit is next to useless.

Does anyone know how these kits behave when they get old? Just wondered if this was the cause of the big difference?

[WallyBrew]

Cheers for that, WB!

Sodium in my tap water has been about 10 to 11 ppm in every water report, if that helps?

I appreciate that home kits are not going to give very accurate results. But going by the Murphys figure, the home kit is next to useless.

Does anyone know how these kits behave when they get old? Just wondered if this was the cause of the big difference?

Given your sodium figure and the one I have calculated and the calculated alkalinity I would say that the home kit is EXCEEDINGLY GOOD and that it is the MURPHY FIGURE WHICH IS NEXT TO USELESS

[OvenHiker]

Given your sodium figure and the one I have calculated and the calculated alkalinity I would say that the home kit is EXCEEDINGLY GOOD and that it is the MURPHY FIGURE WHICH IS NEXT TO USELESS

The other Murphy figures are pretty much in the same "ball park" as my water company reports, it's just the alkalinity measurement that surprises me. Perhaps, as you say, it is the Murphy alkalinity figure that is suspect!

Thanks for your responses WB!