A day of devastation

I don't think weedkiller would work that fast. How much potassium bicarbonate did you use? I usually stick with a 0.5% solution, so 5 grams per litre of water. Did you also use soap?

1 tablespoon to one gallon, ½ teaspoon soap (a bit of hand wash which might be the culprit) and a  ½ teaspoon of veg oil.  Whether its the soap or weedkiller residue I'm still stuffed.