dutchy101 if you were able to produce a formulation that is guaranteed to be safe to hit the sweet spot between non scaling and non corrosion for service boilers, this could really be a good selling point for the Skuma.
SkumaWater Also I believe the formulation you currently use is not ideal since adding sodium bicarb will only help with alkalinity problem but not the corrosion problem. I might be mistaken
It’s not possible to achieve a sweet spot. In service boilers, due to what they are used for, the saturation will increase over time, so something perfectly balanced at your operating temperature would only really be balanced for the first few drinks you steam milk for. Similarly, as the temperature swings from room temp to the set temp in both brew and service boilers, the equilibrium changes - it’ll be more or less corrosive depending on the temperature.
If you insist on adding hardness to the water it’s best to aim for non-corrosive and non-scale forming at your typical brew temp (e.g. approx 105c for a 95c setting at the group, though this is machine-dependent) and just accept you’ll need to give the service boiler a light descale. You might also add hardness and alkalinity from non-carbonate sources such as citrates.
Corrosion is much more complex to the point I’m not comfortable discussing it. I believe the addition of alkalinity to control pH and stop water from becoming too acidic is the main thing to do, but the absence of cations e.g. Calcium and Magnesium will leave the water more aggressive as it will seek to create an equilibrium regardless. Dissolved gasses like Oxygen, Hydrogen and Carbon Dioxide will also cause corrosion - but alkalinity will at least grab the hydrogen and stop it attacking the metal, and resist pH changes from carbonic acid. Scale will form a protective film, but in the presence of sulfates you can have bacterial build-up with the scale causing biological corrosion - the bacterial accelerated reduction of sulfate producing hydrogen sulphide.
A solution to prevent corrosion with soft water is to use corrosion inhibitors like sodium silicate which will create a thin film on metals that doesn’t build up and thicken like carbonate scale - and it will disappear if you stop treating the water as in it needs constant application as it doesn’t adhere to the metal permanently. How this will affect the taste of water and coffee - pass.
SkumaWater The main difference between the Coffee Balance and let’s call it “Espresso” for now, would be the addition of Calcium hardness to protect against corrosion.
Calcium hardness wouldn’t protect against corrosion.
I’m assuming this would come out as about 40mg/l KH and GH. Would be fine in a brew boiler but scale in a service boiler if it’s more like 50 KH. Anyway, as said, there’s not much point trying to stop scaling in the service boiler with carbonate sources.