so i think i solved what was going on here. bottom line is, don't trust calibrating your refractometer with RODI (like the manufacturer recommends!). I bought 35 ppt reference solution, and with a refractometer calibrated with RODI, i was reading like 33 ppt! It all made sense too, at 0.5 cups per gallon of mix, i was having to dilute to get to what I thought was 35 ppt, but was in reality much lower, which led to my very low stats. I haven't checked a fresh batch yet to see what alk/mg/ca are, but I bet they are closer to correct.