Troubles raising KH

[Douglas]

I'm having issues raising my KH to a desirerable level. I've switched products from B-Ionics to bulk reef Sodium bicarbonate, about 3 months ago, and still can't raise my KH past 6 dKH. With all the instructions i've been reading, i'm still having a very hard time raising the KH. I've increased my doser, and manually added more, but i'm still getting low readings.(brand new test kit). What can i do next? My corals are suffering.

HK today...5.4dKH
Cal....400
mag....350