Hi all,

Long time lurker here. Last year I plumbed in my Lelit Bianca. Have been using a Brita purity finest (sodium softener) for a year now. Since it was time to change the cartridge I decided to give the Brita Quell ST a try (a C50) since it is cheaper, takes less space and I was curious to see if the taste would improve.

I got myself a titration kit and got the following values from my tap water:
GH 161 - 169 ppm
KH 149 - 157 ppm
PH 7 - 7.5

According to my water company chloride is at 27 ppm, sulfate at 21 ppm.

According to the Brita manual a bypass of 50% would be required. I did another test. This time straight out of the filter with the flush valve (after running 5 liters) and got:

GH 81 - 89 ppm
KH 118 - 125 ppm
PH 6.5 - 7

Ran another test, but this time with 40% bypass:

GH 46 - 54 ppm
KH 81 - 89 ppm
PH 6 - 6.5

The low PH made me worry the water would be too acidic and potentially corrossive. So I set a bypass of 50%, drained the boiler of my Bianca as to replenish them with fresh filtered water. I then waited a few hours and from a cold machine tapped some water and ran a test. With 50% bypass I got the following:

GH 81 - 89 ppm
KH 134 - 141 ppm
PH 7 - 7.5

The higher PH is probably the result of the Co2 wearing off, which is more present in the water straight out the filter. I am thinking these values are a bit high and probably will form scale. Which is what I am trying to avoid as much as possible.

I wonder if I could get away with 40% bypass, but I am worried the water might be too acidic. The GH and KH would get me more in the range to avoid scale forming (50 ppm GH and 85 ppm KH), but the potential 6 PH worries me. I am not sure how this would come out of the boiler as I only did a test straight out of the filter. Also I am not sure why the KH is higher, post filtering, instead of the GH.

Any insight or suggestions on these values and what bypass to choose would be greatly appreciated.

Would be much appreciated if anyone could chime in.

I've been reluctant to reply because I'm not sure I have reliable advice here - it's a tough call. But FWIW ...

Summarizing your numbers:
Tap
GH 161 - 169 ppm
KH 149 - 157 ppm
PH 7 - 7.5

40% bypass
GH 46 - 54 ppm (115 reduction)
KH 81 - 89 ppm (68 reduction)
PH 6 - 6.5

50% bypass
GH 81 - 89 ppm (80 reduction)
KH 118 - 125 ppm (31 reduction)
PH 6.5 - 7

50% bypass after a few hours in steam boiler
GH 81 - 89 ppm (80 reduction)
KH 134 - 141 ppm (15 reduction)
PH 7 - 7.5

Given these numbers It does appear that the Quell ST has some sort of buffering media, likely a mix of WAC and conventional SAC resins. (A pure WAC resin typically reduces hardness and alkalinity by an equivalent amount.) As you say, the higher pH in the water that has sat in the boiler for a few hours is likely due to dissipation of CO2 into the air (and some out he anti-vac valve) of the boiler. This effect would not explain the higher alkalinity in the boiler water, but that may just be variability of the system - blending valves are not precise, and contact tiime and flow rate in the filter can have a big difference.

I can't say that I have clear advice here between 40% and 50% - it's a coin toss deciding between corrosivity and limescale deposits, and the corrosivity issue is key here because of that borderline high chloride ion. I think I would be tempted to go back to your original Purity Finest (conventional SAC resin softener that reduces hardness to very low levels but leaves alkalinity and pH as-is.) If I stuck with this one I think I'd choose the 50% bypass and keep an eye out for scale, and descale the machine if/when needed.

Thank you very much for your reply.

At this point I'd rather be safe then sorry. I've decided to, as per your advice, change back to a SAC filter (the Purity Finest). This will give me a water quality that is less than ideal (249 ppm TDS), but for me is the most worry free option for machine health.