Fermenting grape juice in 2qt jugs. How long?

[Aróchito]

Hey folks,
Got two 2qt bottles of flavored grape juice here. Put red star rouge yeast with half a teaspoon of nutrient and some added sugar water. They've been fermenting for six days and it looks like the fermentation process has died down significantly. Any idea how long the ferment will last? Such a small quantity. Thanks in advance.

Also, if I add some extra sugar water, will it wake up the fermentation at all? Thanks. Added some visual aids.

 

[WBB]

Did you just blindly throw yeast and sugar into flavored grape juice?

 

[Aróchito]

I wouldn't say blindly. Only ingredients in the juice are natural flavor and Potassium Metabisulfite which from what I've read does not get in the way of fermentation. That being said, I did throw yeast and sugar into flavored grape juice.