I'm not sure what you mean by all natural.
As far as magnesium, it is consumed at a relatively low or slow rate, which possibly can be maintained by the magnesium in your salt, and with frequent water changes. With a Mag of 1460, it would appear that this is the case.
Now as far as the other two guys we need to grow calcified corals.....that is alkalinity and calcium....they can't be maintained with a well established tank by water changes alone. You might be able to get away with it when you have but a few frags, but eventually you'll need to do something to maintain these two guys.
The three most common ways of doing this are:
Calcium reactor
Kalkwasser
Two part dosing
And that is where I'm scratching my head of whether or not you consider any of these "all natural."