Renewed effectiveness of the RO/DI is possible. I'm sure Russ set you up better. But I'm thinking more along the lines of the Ca, Mg, Alk.
It is possible that the low Ca and high alk is causing some issues. I'd do a good sized water change and try to balance them out a little. FWIW, when I did carbon/aminos/food, I ran on the high side (Ca 450 to 500 and alk 11.3 to 11.8, MG 1350 to 1450)
It's a shame how unreliable those Aquamedic Dosers have become. I really think Jon (jhale) is the only one who has 2 pumps that consistently dose equal amounts.
Fred is very much convinced thet to much stability is a bad thing (murphy is going to get you) but I disagree with him in that aspect.
Happy New Year to you Ken. I'm sure a water change was the last thing you wanted to hear, but that is the first thing I do when I see parameters for Ca, Alk or Mg go out of whack.