Hm... could be. The salesman said it was DuPont. Maybe he's wrong.
I am using AquaFinesse's chlorine dispenser. However, I am only 0.5ppm. They recommend 1.5. I've added a dispenser to try and get that up there. However, it does seem kind of contrary to the product to start pumping chlorine into the spa, something we wanted to go away from. Perhaps ozonation is the only way, but then I've heard there are dangers there.
I think the answer is God's answer—find a mountain hotspring. :-)
By the way, the hot tub in our house is probably 25 years old. How the heck do I figure out how many gallones/litres it holds? AquaFinesse is pretty precise when it comes to how much to add based on volume...