Dry Hopping: Knowing when to stop amidst sour green beer taste.

I'm dry hopping a bavarian hefe with 2 oz. of summit in a keg (trying to extract the onion and garlic charactaristics, it'll make since when I post the recipe after I perfect it). I tasted it fresh out of the primary (after 15 days), and it had a pretty good flavor already, albeit pretty sweet tasting.

It's been dry hopping for about a week now (4 days at about 70 degrees, then 3 days in my fridge, hops are hanging by dental floss in a bag with marbles), but the beer has become very tart. Though there was some funny looking stuff on top in the fermenter, I don't think its infection because it has a fairly different taste than vinegar and smells of apples. In fact, tasting it is like biting into a very VERY green apple, so I'm assuming its some sort of green beer taste.

My question is, could the hops be adding to this tartness, and if not, whats some good advice and how to know when I'm done.

PS: I have a glass of it here to describe it, and the tartness seems to be subsiding as it warms...

https://www.homebrewtalk.com/f39/pond-scum-how-much-air-too-much-406622/

Pics of said beer in fermenter.