Potassium carbonate
K2CO3
Deacidifier, stronger per gram than the bicarbonate.
Typical dose
Bench-trial; more alkaline than potassium bicarbonate, so easier to overshoot.
When to add it
Finished wine, then cold stabilise.
In practice
Does the same job as potassium bicarbonate and reaches further per gram, which also makes it easier to overshoot into a flat, soapy wine. Most home winemakers are better served by the gentler bicarbonate.
Linked faults are the ones this addition either treats or, used wrongly, causes. The fault page says which, and whether it can be undone.
Others in acids and deacidifiers
Tartaric acid
Raises acidity and lowers pH using the acid grapes already contain.
Malic acid
Raises acidity with a sharper, greener sourness than tartaric.
Citric acid
Small acid corrections and iron-haze prevention, but microbially unstable.
Lactic acid
Gentle acidity for fine-tuning, especially after malolactic.
Potassium bicarbonate
Deacidifier: lowers titratable acidity and raises pH.
Calcium carbonate
Deacidifier for large acid reductions, via the double-salt method.