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Pool store worker here, long time lurker, this issue has me stumped and figured bounce it off some brains in the interwebs. New spa customer with nature 2 stick in filter. Activated correctly with low dose of dichlor. Adding small amount of oxidizer (monopersulfate) few times weekly as maintenance. Both husband and wife break out in rashes. Watertest shows VERY HIGH Total Chlor/Brom levels and everything else in balance including low free chlor. (strips) With the low free chlor and the high total I was tempted to think that the rash could be caused by chloramines. Also from experiences, sometimes the total strip can light up do to oxidizers which in large amounts surely could irritate skin. No idea which it was or if it was something else. So, we did what any good store would do, especially with a rash situation, told them to drain, clean and refill. Gave them a new N2 cart and told them to add 1tbsp of dichlor as directed in the instructions. They brought in another sample today and it appears that the exact same thing is occurring. The pH and Alk were great as was the hardness. The Free Chlor was a 1.5 which is very strange for only 1 tablespoon after 24 hrs. The total Chlor was rocketing up. Obviously told not to get in but this has me perplexed. Thanks for any thoughts.