Grammatophyllum elegans Leaves turning yellow

[mjf45322]

Help, I need to know what I am doing wrong with this species plant. I got one from Hawaii 3 weeks ago along with 2 different clones of Gram. Scriptum. The Elegans new growth rotted off and the growth/bulb next to it has its leaves all turning yellow. I got another plant from the same dealer and since it was out growing its pot I moved it into another 12" pot big enough for 2 more years growth . I noticed today that the tip of one of its leaves is yellowing.
I grow in a greenhouse with 65% humidity. I have the plants in a area wher they get max. light with day time temps of 90F and night temps of 55F.
I water 3 times a week normally overhead, but have the plant where it will not get soaked. It gets a light mist from my fogger when its on.
The Gram Scriptums are in smaller pots and get soaked when they are watered and they are happy. Should I treat the Elegans the same. Should I try growing it in a smaller pot.
The grower in Hawaii grew it in a potting soil with a little bark. I was afraid in my climate of root rot so I repotted it into a med. bark/perilite/characoal mix.
Should I allow it to get soaked when it is watered eventhough its in a huge pot with good drainage.
Thanks,
Mike