Potatoe Wine

My potatoe wine has finished brewing but it’s very sour.
My best guess is that it’s below 2,5. I want to add doublesalt to lower the acitity. But I am havi trouble figuering out how many grams of double salt I need to add.

i have 20 liters of wine.

Probably would be best to measure out a couple exact portions of wine to each one add different amounts of salt keeping track so then you can scale up.