Wow, it really would depend on how much water your tub holds and then use the recommended mixture. I usually just fill a full size cooler 3/4 the way full, and add a level scoop. 24 hour soak and off they come. I wouldn't put more than 2 scoops in a tub.
You may want to re-think doing all the bottles at once however. You're going to have to rinse them really well after soaking them to get the Oxy residue off. Maybe break up the load into 12's or 24's so it's not so hefty.
Ize