Raising dKH in 12g Nano

[Snaz]

I bought and tested for the first time a dKh test kit. My 12g nano is at 5.1 dKH so it needs to come up a couple of points.

I have zero experience with dKH but I know it must be raised slowly. My tank is display and three compartments behind a false wall, no sump.

Corals looks ok, sps is new to me(six weeks) and while there is PE the growth on two pieces is rather slow or no growth. How best to raise this please? Any hazards?