katkat wrote:Based on this, bypass 3 might do the trick: KH will be at ~50 (48%) and Cl at 23 (13%). Per Aqua Cl usually hover around 100, so it should be better most of the year.
Filter capacity at bypass 3 given my TDS would be 530 gallons, which should be enough for the machine 0.5 gallon/day. I might even add a drinking water tap (to be also used for convenient flushing.) Filter would be replaced annually, per specs.

That all seems reasonable to me.

katkat wrote:Not sure what the impact of the low output PH at bypass 2-3 is? It's lower than La Marzocco's recommendation.

That low pH is a little surprising given that the KH measurement is not alarmingly low. If you have good alkalinity I think you can get away with lower than recommended pH.

katkat wrote:PS - I sent another escalation email today to Pentair but I am close to giving up.

That is disappointing. At one time we had water experts from Pentair contributing here on HB, but that's over 10 years ago now.

katkat wrote:Also - I ignored the comment about the TDS calibration factor for now, hoping that it will somehow magically go away so that I will not need to take another thing into consideration

I agree, nothing to quibble about here.

FWIW, These meters measure conductivity and convert that to TDS using a factor. The inexpensive ones that most everyone uses (including the ZeroWater TDS meter) use a factor that multiplies the measured conductivity (in micromho / cm) by 0.5 to display a TDS ppm. That's a good factor for sodium chloride. Fancier meters let you use other factors that may or may not be better for natural freshwater, with the most popular alternative using a trademarked 4-4-2 calibration solution that gives you a factor of about 0.65. Not a big deal because neither one is necessarily right for any particular water. The old SCAA standard that recommended 150 PPM used a 4-4-2 calibrated meter. If you were to use an NaCl calibrated meter on that 'ideal' water it would read 115 ppm rather than 150 ppm.

homeburrero wrote:That low pH is a little surprising given that the KH measurement is not alarmingly low. If you have good alkalinity I think you can get away with lower than recommended pH.

So if the low PH is not a concern, then I feel I have a good chance with this filter. I will give it a shot and report! Expecting the new machine in the next few weeks... Thanks again!

PS - I ended up calling Pentair tech support only to get useless info. The tech said 10% of the TDS/Cl in bypass 1, 20% in bypass 2, 30%/3, etc - which is not in line with the measurements by Chris.