humidity tray? to be or not to be?

[johanna orchid fever]

i have about 7 dendrobiums and i'm having a problem with them they seem to be spotting yellowish leaves and i've read that it could be too much direct light or water but niether have i done for them there dry as sand and lighting is very filtered i have them on a humidity tray and i dnt seem to have such good roots...help i dnt wanna loose them....i give them so much attention as far as keeping there light filtered and i use fertilizers on them once a month i dnt know wat i'm doing wrong....could my house be too dry for them? i live in louisiana and it's cold outside so there in doors. how can i find this out without having to pay so much money....shud i use a humidifier?
any answers are more than welcomed...thanks