You have a lot of reading to do. Since the tub was used by someone else, I would follow Nitro's decontamination guide that's stickied in this forum.
TA stands for total alkalinity and has a direct relationship with PH. You need to get this relationship balanced before proceeding with sanitation/other chemicals. Get a good water testing kit first of all. TA should be in the 80-120 range and PH should ideally be 7.4-7.6. TA can be lower if that's what is needed to get the PH in range, but PH will be more volatile when TA < 80, so small changes once down in that ALK range could have large effects. Higher PH can cause scaling while lower can cause corrosion.
I use Chlorine and over 50% of hot tub owners do the same.
I'm relatively new at taking care of a tub, but I've read so much material in the past 2 weeks that I feel like a new man. If you are going to manage a tub, you have no choice but to read and learn how to operate it, otherwise bad things can happen. I recommend reading and trying to understand everything that user "ChemGeek" writes.