Measuring water GH - drops vs meter

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mathof
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#1: Post by mathof »

I've been using a Skuma RO machine, remineralising with Skuma's Coffee Balance infusion. According to the API drop test my GH is around 100ppm and KH around 60ppm. (I say "around" because it's difficult to tell after how many drops the water has actually changed colour sufficiently to stop adding drops.)

What confuses me is that the same mineralised water reads 37ppm on my TDS meter. I don't think the the meter is faulty as it yields expected readings when testing Volvic and tap water.

Do these contrasting results make sense?

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homeburrero
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#2: Post by homeburrero »

Skuma's website claims (here) that their Coffee Balance adds about 20 ppm as CaCO3 magnesium and about 11 ppm as CaCO3 bicarbonate. So if no other hardness or buffering minerals are in there you expect a GH of about 20 and a KH of about 11. That's below what you can easily test with an API GH & KH drop test. Make sure your kit reagents are not expired, and perhaps try again with a 10 ml sample (with a 10 ml sample it should be about 2 drops for the GH and about 1 drop for the KH)

Skuma is not at all clear about what exactly are their minerals; I think it's likely a mix of magnesium chloride and sodium bicarbonate, which at 20:11 GH:KH would come out to around 38 ppm actual TDS and would read about 35 ppm on an inexpensive (NaCl calibrated) TDS meter at 25 ℃.

(from https://www.aqion.onl/show_ph )


P.S.
Given the somewhat low alkalinity, and the possibility that you'd have about 14 mg/L of chloride ion from magnesium chloride I think it might be prudent to add a little more bicarbonate to this water.
Pat
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mathof (original poster)
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#3: Post by mathof (original poster) replying to homeburrero »

Thank you for your reply to my initial query. I've repeated the API measurements with 10g samples. The mineralised water results are now: GH 5 drops (49 ppm); KH 4 drops (39.2 ppm). The TDS measured by an inexpensive digital meter is 72 ppm).

Out of interest, I measured the TDS of the RO produced by the Skuma from my London tap water (~250 ppm); it reads 36 ppm.

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homeburrero
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#4: Post by homeburrero »

mathof wrote:Thank you for your reply to my initial query. I've repeated the API measurements with 10g samples. The mineralised water results are now: GH 5 drops (49 ppm); KH 4 drops (39.2 ppm). The TDS measured by an inexpensive digital meter is 72 ppm).

Out of interest, I measured the TDS of the RO produced by the Skuma from my London tap water (~250 ppm); it reads 36 ppm.
I assume that this 36ppm reading is from the RO and with no mineral infusion. If so then it all adds up pretty nicely - - you are getting about 36 ppm of conductivity from your tapwater and about 36 ppm of conductivity from the minerals injected from your coffee balance bottle.

That remin + tapwater sum is bumping you up to the GH:KH of 50:40 ballpark, which are pretty good numbers for hardness and alkalinity - probably little or no limescale as long as you don't let the water become over-concentrated in your steam boiler. If the Skuma's magnesium is from magnesium chloride, that may not be ideal though. London Thames water has maybe 30 - 50 mg/L chloride ion, so you may be getting a little (5 ppm or so) in the filtered tapwater, which is not enough to worry about. But it would be best if the mineralizer didn't add more. You might ask them (Skuma) how much chloride ion is in that coffee balance formula.

P.S.
You may be able to find a complete analysis of your tapwater for your postal code here: https://www.thameswater.co.uk/help/wate ... er-quality.
Pat
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