I have heard some problems using potassium carbonate (K2CO3). Use potassium bicarbonate (KHCO3). I do not know how much to use, though. Probably very little.
How did you find out that .12 grams of K2CO3 increases the K in 20 L to 3.39 PPM, i had a similar number to you, i came up with 70 grams, but my math was complicated. i know the amount of K2SO4 required, i then found out the mole weight of both compounds, derived the mole weight of K on each of the compounds based on the percentage and then did the math from there, I know there has to be an easier method as mine is very probe to lots of error. Thank you againHi fplata,
It's been a while since I did ppm.
0.12 grams of K2CO3 will increase the K in 20 liters 3.39ppm
Therefore 0.12 grams X 500 (60 grams) of K2CO3 in 500 ml of water will raise the K2 0.12 grams or 3.39ppm per ml. in 20 liters of water
I do not know if you can dissolve that much K2CO3 in 500 ml of water but that is what it would take if my calculations are correct.