Adrianto,
This tank is recent and I´m only using a Kalkwasser stirrer, but as you mentioned, the corals are growing ok (some fast, some a bit slower).
As regards my parameters, before leaving the tank at my father´s care, when I went on holidays. it was kh: 9.5º dkh and calcium around 440.
When I came back (3 weeks ago) , it was kh: 5.5º dkh (!) and calcium 360 (something went wrong...)
Some corals started to receed a bit, but didn´t die
I didn´t panic, changed 30% of the waterand doubled the amount of kalk in the kalkwasser stirrer.
Things are comimg back to normal and this Saturday, it was: kh 7.5º and calcium 400.
But in 6-7 months time or so, when I set up the calcium reactor .. I hope to see some real growth !