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That is really odd, I wouldn't scrub it, at least not very hard. Give it a day or so and see if it goes away. if not you might drain down and I would use a spray type brake cleaner on it...You have a lot of iron in your water?
That stinks man. I did some googling and it seems like some people try Vitamin C (ascorbic acid) to remove metal stains. I don't know if that will help but that may be worth some research.
When you run your hand over the spot does it feel like a build-up or does it feel smooth like the tubs surface?
Dealer did not tell you to add chemicals with jets on?
Absolute first thing you do is Vitamin C.
a light acid scrub with a Mr Clean Magic Eraser should take it right off