Photos on a.b.p.o under subject line Neostylis Lou Sneary help!

It's mounted on cork with a drop of sphag moss. As you can see, I left the
roots exposed because I blieve that the roots need to get photosynthesis
from the light and need good air movement. The plant however isn't looking
good and I'm not really sure what's wrong with it. When I got it about 8
months ago, new roots growth began almost instantly. I mounted it on cork
and nice healthy roots began to grow. I kept it on the southern side of the
house where it received some direct sun in the morning and mid afternoon.
It's the warmest side of the house and the temps in the winter can reach
about 78 - 80 F. I water it when the roots are gray and dry to the touch.
Feed it with 1/4 strength about twice a month. The plant is declining (I
think). Some of the leaf tips are light brown and hard to the touch. Other
leaves are loosing their green color, in fact I had to remove the top leaf
because it lost it's green color all together. This little guy is just too
nice to loose and I would appreciate it greatly if anyone has any suggestion
as to what I should do to save it.

Thank you in advance,
Mariana