Just whip in some more o2 and check gravity. It is slow and the yeast needs the o2 in such a harsh environment. When gravity reaches your mid point then add more nutrient and introduce more o2.
I think it's a great idea regardless if certifications or not. Being a home brewer I don't know anyone but my family that home brews and it would be nice to get a none bias opinion on my brews. Good job guys keep it up.
By stirring it vigorously it will degas the cider and release the so2 from the mix. This will look like small bubbles rising to the top. The larger bubbles will be co2. Just don't introduce o2 into the cider this is bad, what you can do is use a cut wire hanger attached to a drill and this will...
Welcome to brewing!! Now as said campden is for unpasturized and non preserved juices. Since you are using store bought no need. Tannins are not really needed for cider. There is enough in the juice to give it it's mouth feel that it needs. The strong sulphur (rotten egg) smell is stressed...