After reading the insanely long water FAQ, my understanding is that as water is heated, the maximum amount of Ca and Mg that can stay dissolved goes down. If the water you use contains more than that maximum, the surplus will come out as scale.

In the FAQ there are some formulas to compute at what hardness level we will see scale building up in the machine, but it depends on some assumptions and I thought that in practice it is better to measure what that level is. What I thought was, if I fill up the machine with tap water and let the machine heat up for an hour or so, then just collect some brew water and some steam boiler water, measure the GH and that's the number. To collect the water from my HX machine I switched off the machine and then just used the pressure that builds up inside to push the water out, so there was no mixing with fresh water coming in the machine.

My test results are:

tap water:
GH = 8 dH
KH = 8 dH

boiled water on the stove:
GH = 6 dH
KH = 8 dH

brew water from HX machine:
GH = 8 dH
KH = 8 dH

boiler water from HX machine:
GH = 4 dH
KH = 8 dH


If I understand the formulas correctly from the water FAQ, with a KH of 8 dH, a GH of 8 dH is only possible at room temperatures and for temperatures >95C the GH would already be lower than 0.5 dH.
So I was expecting to get close to 0 or 1 dH hardness out of the machine or the boiled water on the stove, but from the test it seems like with my water 8 dH is safe for the HX and 4 dH is safe for the steam boiler. Would this be the right way of thinking, am I doing something wrong or what else could be making such a huge difference with the theoretical numbers from the water FAQ?

You have a very high kH which will cause lots of scaling. Rising temperatures increases scaling i thought. Not sure what you're actually asking

brianl wrote:You have a very high kH which will cause lots of scaling.

I am not sure how that answers my question. Here is the short version:

From my test results I conclude that a GH of 4 dH is safe for the boiler and 8 dH is safe for the HX, is this correct and if so what could cause the big difference with the theoretical numbers from the water FAQ?

Did you factor in kH, alkalinity? Both affect scaling.

Neither of those will reduce scaling to zero so not sure what you mean by safe? Your kH level isn't even on Jim's chart for safe, non scaling hardness

My kH is 50ppm so I can use 90ppm GH water without scaling at 95 degrees. That what you're talking about?

18 ppm = 1 dH

With safe I mean that no scale will form. If the same GH goes in and comes out of the machine then no scale has formed, irrespective of the KH, is that not?

Right, my value is off the chart, but I can still use the formulas to compute the corresponding values. With such a high KH, the "safe" GH would be <1 dH, but how can I be getting 4dH out of the boiler and 8 dH out of the HX?

You need to factor both kh and GH. Scale is based on both.

I use a double boiler so unless hx machines work differently?

I don't think your measurements out of the group are relevant in scale disposition. Scale in the boiler already would affect such a measurement I would think.

brianl wrote:You need to factor both kh and GH. Scale is based on both.

I use a double boiler so unless hx machines work differently?

Yes for theoretical calculations you need the KH to compute what is the safe level of GH.
But I am arguing that in practice you can just check the GH as any scale that forms inside must drop the GH value.

That's not true based on my understanding. For the same reason putting calcium rocks in a fish tank will increase the GH of the water. The calcium doesn't just disappear.

brianl wrote:That's not true based on my understanding

And why is that?