Neither is really a trace element. I'm sure that is just a matter of terminology. Trace elements include things like strontium & manganese.
You add lime (kalkawasser) to supplement calcium and raise pH. You add baking soda to raise alkalinity. Its not really an either/or situation.
To the best of my knowledge, no one has been able to find pickling lime in SA. There was a thread recently on some places to get it in Austin and in Kerrville.
I guess we need to start thinking about repeating the chemistry talk.
Gary
125 SPS, 75 gal. LPS/softie reef, 9 gal. Nano