Try checking your alkine levels, are you using chlorine or bromine? Try and shower before getting in the hottub, Body persperation can cause your levels to change, So can beer and wine. :)
Wear Gloves and a mask. You should be able to tear out the old stuff in a couple of hours. once you get the majority of the old stuff out and are finished for the day spray down the area with bleach and let it set over night. This will kill any mold that is left. Be sure and remove all dry-rot...