Vanda roots wither

[Kollba]

Some months ago I got a Vanda that looked very good, from my mother-in-law. Strong fresh leaves and 4 thick roots. I mounted it and it seemed to like its new home, but after 6-7 weeks the lower leaves started to get yellow and fell off. The remaining leaves looked ok but they had got more and more wrinkled, just as it was underwatered. I started spraying it with water 2-3 times a day, but nothing changed except for that two of the roots started to grow offshoots. I tried soaking it over night a few times and then I put strips of fabric on two of the roots to keep them wet 2-3 hours. Once a day I soaked the strips at the same time as I sprayed the arial roots with water. There is one new big root growing but I do not think it looks very healthy and all the small offshoots have withered.
What am I doing wrong ?
And... I have about 35 vandas. All the bigger ones, but one, has very few roots but they are not growing any new roots. Is there a season for root growing or what ?
I live in the tropics and this time of the year there is no rain, 28-35 C temp (80-95 F, cool in other words) and the humidity is about 50 %.