osteoblasts build bone thus require Ca2+ which is supplied by calcitonin ( which tones down Ca2+ in blood)
osteoclasts break bone with PTH ( increases Ca2+ levels in blood). I mean PTH indirectly stimulates osteoclasts to break bone in order to increase Ca2+ levels in blood
hope that helps
The answer is in your question - Yes calcitonin will decrease the Ca++ levels (in the blood). When Ca++ is deposited into bone, it has to come from somewhere (blood). So Ca++ goes out of the blood and into bones. That's why blood Ca++ levels go down.