i broke the knock off of my terminator hunter 6075 arrow and i replaced it with a knock off a terminator hunter lite 6075 and now i am hitting low on my shots. The knock off the lighter arrow seems to grip the string tighter, will that affect my groups? Are there different size knocks or are they all the same size?

Yes, if it releases off the string differently it could affect where it hits. Check out the end of the arrow too, make sure it isn't cracked. The nocks from those 2 arrows are the same.