Distilled white vinegar is the standard for the dosing schedules. It is 95% water and 5% acetic acid.
While were on the subject ,80proof plain vodka is 40% ethanol and 60% water; so it takes only 1/8th as much to equal vinegar's carbon content. Solid carbon sources, like sugar and vitamin C take 1/20th gram to 1 ml of vinegar to get an approximately equal amount of organic carbon.