Do you have a sump? A topoff system? If you don't have a topoff, you'll want to look into that. Try autotopoff.com. This keeps the salinity level [sg] of your tank even, with the evaporation necessary in a reef tank. You can keep a small amount of pickling lime in your topoff reservoir, when you have enough corals etc to HAVE a calcium demand...which you won't at first.
A topoff system is best run from a ro/di reservoir and a float switch. A ro/di reservoir is water that has been run through a ro/di filter, in a bucket, ready to be added to your tank.
At first, your calcium and alkalinity will be satisfied by weekly 10% [2.4 g] water changes with new salt water.
Later, when you need more alk/cal, and once you have some remote idea how much evaporation you have, you can put kalk [pickling lime] in your topoff water and stir it up periodically. [Some use a small maxijet pump that runs on a timer and comes on twice a day for a few minutes.]
If you get beyond this in demand, you can add a kalk reactor, a 2 foot plastic column that has a constant medical stirrer under it, which keeps a certain amount of kalk in suspension, and your topoff water pushes through that chamber on its way to your tank, thus exchanging pure fresh water for kalkwasser [kalked water] and keeping up your alk and cal to a very great extent.
If you choose not to use it, at the point when you would begin using it, you can buy something like Kent dkh buffer and Kent Turbo Calcium, and hand-dose into some water-flow area, after diluting it in a measuring cup. You can, alternatively, put ONE of those two elements into your topoff water, if you know your evaporation rate AND your daily demand for the stuff. You cannot add both together, because they mix to create a nasty snow all over everything---not good.
This is a complex answer, and I don't blame you for being puzzled. A kalk reactor is a wonderful thing for a 50g and up tank; it may be a bit of overkill for a nano.
I'm fairly new to the kalk thing myself, and I invite others to chime in on this: I've never used it without a reactor, and have a half-notion how its done via the reservoir---I tell you the best I know and hope to be right.
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