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Hard to say what that is but I wouldn't use Simple Green or Dish Soap to clean a hot tub, those are only going to leave residues. Are your filters clean? Buy some granular dichlor (chlorine) and hit it with a heavy dose of 3-4 ounces. Sometimes it can work better than bromine, especially if you're using an inactive sodium bromide.
Whatever sanitizer you are using (Bromine?), turn off the power to the unit for a bit and leave a tablet there. If the slime dissipates and and doesn't come back to that area its being killed by said sanitzer and is likely organic growth. (Turning off the power solely to allow the tab to sit there and not be moved from the area by the turbulence of the water).Try that and if not you at least can cross that off your list. Check the cover and behind jets in the jet housings, behind headrests, and any other nook/cranny you can find for any green slime too. Its best to wipe the tub down with white vinegar/warm water mix to clean the shell. Also if your bathing suits have come from somewhere else (Pool, beach, lake, stream, etc) there is a chance that they could transport algae spores into your water.Just some tips to help you identify. It may not be that at all but you got to start somewhere. I hope this helps. Good luck moving forward.
Use a purge or hot tub plumbing cleaner to remove any traces of biofilm.