Mandarin Sunset

Notices second plant had small spots on bottom leaves thought it was from water burning on the leaves as it was very small however 24 hours later it got a bit worse. Researching suggests it’s either rust fungus or cal mag deficiency but it’s only appearing on 2-3 of the lower leaves of the plant. I treated both plants with advanced nutrients voodo juice b50 and sensi grow 1/2 as well as mammoth p Having issues with temp /humidity as I can only choose high temp with low humidity or great temp with humidity ranging from 50-67