I tend to follow Tanaka's experiences. He mentions that 3 species in particular (from parvisepalum) love water and you never let them dry out. These are armeniacum, delenatii, and emersonii. He does not mention hangianum so at the moment I'm lumping it with these 3. My delenatiis and armeniacum are doing MUCH better now that I water more often. I only have 2 emersonii in the ''hot box'' and they are doing ok. Certainly better now that they get more water. Same for the hangianums. You have to experiment with the mix. Straight bark works for some but not for me. Even bark mixed with perlite or stones just does not last long enough. As it rots it takes the roots with it and I'm back to square one. The colour of the seedlings is also a good guide that you are on the right track. Yours do not look good. I would guess the roots are probably non-existent or very weak and if you don't do something soon you will probably slowly loose all of them. So, if you are going to water a lot you need a mix that dries out quickly and is well aerated. A very coarse mix does not work either. It dries out fast but there is nothing for the roots to work with. A constantly moist mix (one that hold moisture for a long time) just does not seem to work the same as a mix that dries rapidly and that you have to water a lot. This is my experience of course so it could be different for others. This year I have decided to largely do away with the bark and use tree fern fibre/charcoal/sphagnum/polystyrene/bark about 2 parts/1part/1part/1part/1/2part. And I add some kind of calcium carbonate for the limestone growers. (Just to stop the mix getting too acid)
I pot very loosely at the bottom of the pot and firmly around the base of the plant. You cannot do this with anything but a fibrous mix. Also I melt some vertical slits all around the pot sides. With good air, this arrangement dries out in about 1 or 2 days. I have a theory that the moss and tree fern fibres act as a wick to the outside atmosphere removing water faster than bark does even though it is ''finer''. You will have to experiment with mix that will suit your conditions and remember that it will take 12 months before you can judge it. But one things for certain, you should repot those seedlings into a much smaller pot (probably 1/4 the size of that one) into a fresh mix and try to get them back to a darker green which is what they should be. if you cant find tree fern, maybe try bark and polystyrene with some chopped and screened sphagnum with charcoal. The ''trick'' is a very small pot that dries out fast or a larger pot with plenty of holes in the sides.
I'm still experimenting. Some people just throw any plant into a pot of bark without much thought and have good success but not me!