Thanks - actually I don't have any coral based substrate or limestone in there as Calgary water is already pretty hard to begin with.
I did figure out it's the source water to blame (lot of limestone upstream).
I ended up cranking the CO2 (2 bubbles per second or thereabouts) to get pH down a bit. The end result is this (funny you brought this thread back to life 5 minutes after I took this picture and was thinking of uploading it):
