BER is not a Ca deficiency issue. That is old, very old research. BER is a consistent moisture issue in combination with the age of the plant. Lots of discussions here about it that a search will pull up. And a FAQ too.

Your MG Potting Mix contains lime which is an ample source of Ca. You just need to work to stabilize the soil moisture levels. Difficult to do in such containers but not impossible.

Dave

Here is a link that might be useful: BER FAQ and discussions

Dave,

You have the patients of Job.
I just wanted to thank you for all the helpful info you freely give.

Make that the "patience" of Job.