If you have a gram scale measure doses and mix into a 5g bucket then test results to establish adjustment values. (what I did)
W/O a scale do leveled mixing spoons 1/2 & 1tsp but realize that compaction and moisture effect the values slightly more than the scale but it's still minor.
The Fraternity of Dirt
If at first you don't succeed,,, keep kicking it RubberSideDownOnTheLanding, 2-75g planted, 5-55g planted, 5-20g planted, 110g w/30g sump, 8-10g, Refugium, doghouse/newbie 2012 update adding table top pleco pans & a 90g (Nutz)
Also, I believe potassium carbonate (K2CO3) adds ~33mg/l K+ along with each 1 degree of hardness added by the CO3 just like K2SO4 does. It works well but you have to understand and want the K+ ratio. lots of extra K seems fine, but plants don't need KH so it's just a pH buffer issue. If you have two or three degrees in your tap I would not bother raising it. Over four degrees can limit some plants. Otherwise K2SO3 is supposed to be a good way to raise KH.