Rootless Zygo--please help!

[Reeses]

I had problems earlier this year with my Zygo. Advance Australia. I got a bit over-excited with semi-hydroponics, and I just plonked it right in even though the roots weren't actively growing. I had just gotten this plant, and it was potted in pure sphagnum. There was nothing wrong with it, the sphag was good quality and wasn't breaking down; I was just convinced the Zygo would LOVE S/H.

Well, so far, it hasn't. It lost most of the roots within a week or so, and I dosed it up on K-L-N, and left it alone for a few months, still in S/H. I noticed yesterday that its new growth had stalled, which made me concerned, so I unpotted it, and, to my horror--all squishy, grey roots! I cut them off and gave it a long soak in some K-L-N solution, and I potted it up today in a mix of fresh LECA and sphag, in a much smaller, more ventilated pot. It's now sitting on a heat mat with some of my other struggling orchids.

I have two main questions: 1) since Zygos tend to be cooler-growing, should I keep it on the heat mat? I thought it might help stimulate root growth.
2) Is there anything else I can do for this plant? I really love it, and I want to do the best I can for it, but I'm still learning. Any tips would be greatly appreciated!