Blind Pete

I bought my spa new three years ago. I have always maintained my chemicals, ph levels, and all prescribed maintenance. After 3 years of bliss, I began this year to experience itching only in my back, where the jets hit me. I changed the water and installed a brand new filter. But the problem persists. I understand it to be diagnosed by others as bacteria infection of hair follicles. But I am doing everything that I always have done, without problems, for three years. The spa salesman mentioned the ozone injector, but said if so, that I would be having to use more chemicals to keep the water clean. This is not the case. I need no more chemicals than I have in the past three years. I use chlorine. I keep the spa at 103 degrees. The chemical balances and ph all test fine. No other areas of skin are bothered, only my back where the jets hit. I tried sitting further away from jets, but no improvement. I am out of ideas.