Cleaning Biofilm from Jetted Hot Tub

I was looking for something to clean our jetted bathtub. I am concerned about using the tub, because when we bought the house, it was unoccupied for a while before we got here, and I have no idea how (or if) the inner parts had been cleaned prior to that. So meanwhile I’m not using the tub while I try to find a suitable way to clean it. I’ve seen many recommendations online for using Cascade dishwasher detergent and bleach, and I’d prefer not to use those.