Dichlor/Bleach (post here: https://www.reddit.com/r/hottub/comments/xaelv3/new_to_hot_tub_water_chemistry/intncoj/)

Dichlor: https://www.amazon.com/SpaGuard-Enhanced-Spa-Shock-6/dp/1754164498/

Bleach: https://www.amazon.com/Smart-Case-Gallons-Chlorinating-Solution/dp/B00KWU1BBU/ (but way cheaper in person at Walmart)