If it were me, I would leave the chemicals alone for a bit and do some water changes. Messing with additives can make matters worse.
Once you get to the ideal dkh
with water changes I would then monitor it to see how fast it drops as well as how fast your calcium/magnesium drop. this will tell you how long your tank can go with just the water changes before you have to supplement.
What is the alkalinity of the fresh water that you put in? Does it drop after it;'s added? or are you starting out with low alkalinity?