Testing Calcium TDS vs Total TDS?

Water analysis, treatment, and mineral recipes for optimum taste and equipment health.
Mike-R

#1: Post by Mike-R »

I'm discussing water softening with tech support where I purchased my espresso machine. I had been using an in-tank softener and seeing what may be fast buildup of scale. The rep recommended that I test the softened water periodically to make sure it's following the espresso machine manufacturer's recommendation of 70 ppm total TDS with as little calcium as possible. I was kind of surprised at the suggestion to test my softened water. Measuring TDS is easy enough, I guess, but my understanding is that I would have to send water samples to a lab to get specific breakdown of calcium ions.

Does anyone really send their post-softener water to a lab for analysis? That seems expensive and unnecessary to me. But I admit that I'm new to water chemistry for espresso machines, so I don't really know. Any thoughts or advice?


(Side note: I'm planning to start making my own water, so this will become a moot point. But in about a year I hope to plumb in the machine with an in-line softener, so water chemistry will become relevant again.)

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homeburrero
Team HB

#2: Post by homeburrero »

Mike-R wrote:The rep recommended that I test the softened water periodically to make sure it's following the espresso machine manufacturer's recommendation of 70 ppm total TDS with as little calcium as possible. I was kind of surprised at the suggestion to test my softened water. Measuring TDS is easy enough, I guess, but my understanding is that I would have to send water samples to a lab to get specific breakdown of calcium ions.

Does anyone really send their post-softener water to a lab for analysis? That seems expensive and unnecessary to me. But I admit that I'm new to water chemistry for espresso machines, so I don't really know. Any thoughts or advice?
One problem with using a TDS meter for this purpose is that it will read the same even after the water has been well softened by a conventional softening resin (where both calcium and magnesium ions are removed, and replaced with either sodium or potassium ions.)

But you don't need to send the sample out to a testing lab - - you can test the hardness yourself using a fairly simple and inexpensive drop titration kit. The cheapest and easiest are the GH & KH test kits sold online and at aquarium shops. The GH is a measure of total hardness from both calcium and magnesium ions, but it's good enough for estimating scale risk. Water is a combination of calcium hardness plus magnesium hardness, and in most natural water the magnesium is a small proportion. Your calcium hardness is always something less than your total hardness.

You can get nicer titration kits from Hach, and also can get kits from them that can separately measure calcium vs magnesium hardness. Most people just use the API kits. The API kit can be 'stretched' for better precision at low concentrations simply by using a 10 ml sample size rather than the normal 5 ml sample. With a 5 ml sample each drop of titrant corresponds to 17.9 mg/L hardness as CaCO3, but with a 10 ml sample each drop corresponds to 8.9 mg/L hardness as CaCO3.
Pat
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Mike-R (original poster)

#3: Post by Mike-R (original poster) »

Thanks for the reply and all the info on the titration kits.

Do you have a rough idea of the conversion efficiency (not sure if that's the right term, but sounds good) of the resin filters? I.e, does it exchange almost all of the Ca and Mg ions? if so, I just can't imagine any purpose of testing specific levels of Ca and Mg in softened water unless it's to get the maximum possible life out of the resin filter. And considering the cost of resin filters vs the cost of titration kits, I can't see how this would result in very much overall cost savings.

I don't know, maybe I'll just use R Pavlis water as my long term solution. It sure would be nice to never have to descale my machine.

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homeburrero
Team HB

#4: Post by homeburrero »

Mike-R wrote:Do you have a rough idea of the conversion efficiency (not sure if that's the right term, but sounds good) of the resin filters? I.e, does it exchange almost all of the Ca and Mg ions? if so, I just can't imagine any purpose of testing specific levels of Ca and Mg in softened water unless it's to get the maximum possible life out of the resin filter. And considering the cost of resin filters vs the cost of titration kits, I can't see how this would result in very much overall cost savings.
The exchange efficiency quickly drops when the resin is exhausted, so you need to do the hardness vs capacity vs volume calculation and replace them before they are used up. Otherwise it depends on the hardness level and the flow rate and would generally exchange 60% - 98% of the dissolved calcium. (See figure 2 of this technical reference.) Typical 140 mg/L hardness Houston water would drop to maybe 5 - 20 mg/L CaCO3 equivalent. This would be for a conventional (SAC resin) inline softener with no bypass.

You could use a total hardness test kit, like a stretched API GH kit to tell you if you've screwed up and overused your softener. I know of a couple of HB members with cation softeners that recommend using a Hach HA-71A kit to verify that their water is at very low hardness levels. Pricey, but will reliably test low levels of hardness.

P.S. [edit addition]
If you are using an in-tank pouch filter, it may be far less effective depending on contact time. See Tell me about these reservoir water softeners
Pat
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