It depends on the calcium demand of your reef. If you don't keep high calcium demand corals than your need will be pretty low. If you run a full blown SPS reef of large colonies a calcium reactor or two part dosing solution, will be up there.
0 (as I've never owned a calcium reactor, I use 2 part)
10
0
Cal Reactor - 7 (a bit expensive but pays for itself in a year)
Phosban Reactor - 10 (essential for good calcification and growth...no more red slime ever! )
Uv - 0