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I haven't added any CYA.
As you have learned from other posts, for every 10 ppm Free Chlorine (FC) from Dichlor, it also increases Cyanuric Acid (CYA) by 9 ppm. Though it's possible that your continued use of Dichlor making the chlorine less effective over months, but it's more likely you weren't adding enough disinfectant after each use or in between uses and the chlorine got to zero which allowed bacteria to grow. That is, if your rash is bacterial and not a chemical reaction or something else. You rash might not even be related to the spa. Does it get worse after an equally hot bath? You might be sensitive to hot water temperature.