Hi Christy,
Youll get it beat,im sure.
I think a large part of the diatoms may be the large water changes you have done,Almost like putting your tank thru mini cycles....
Remember the ones we get when we fire up a tank for the first time?...sort of like that.
Did you notice an increase of diatoms after the first water change?
Kalkwasser would be a good idea,but after your alk has been brought up with buffers,kalkwasser will help to maintain the alk...so if it is low now,it will help only to keep it low.
Instead i would use buffers only and religiously until its back to normal.
Recent lighting changes also make a huge difference.
The Berlin XL should be more than enouph for your present coral and fish load,so if it is working properly with a decent pump i doubt wether that is your problem.
Your soft corals look shrunken,are they always like this ?