I hope the enclosure is well ventilated. I have no experience with Theraphosas, all I know is that they like their sub moist, but they still need good ventilation. And 83% seems quite stuffy... I don't know. @Nightstalker47 might know more on this matter.
You really shouldn't be chasing humidity numbers. Especially in a glass aquarium without poor ventilation, stagnant air will kill this genus faster then anything else. Dont mist, pour water directly into the sub. You may need to rehouse that specimen, but Ill need more pictures of your setup to confirm. http://arachnoboards.com/threads/theraphosa-care-and-info.303033/