Help my oncidiums!

[Outdoorsgalmd]

Hey everyone. I just joined this site today - looking forward to many discussions to come!

I am a part-time (very part-time - busy job) beginner orchid enthusiast in Baltimore. My house is new construction within the last couple of years, which is relevant because it is super Tyvek-wrapped and has very little air flow as a result. It is so tight and energy efficient that they install a fan that automatically turns on upstairs to circulate the air enough in the top floor. They also installed windows with UV protection to protect furniture and whatnot. This is great for utility bills but not so great for indoor orchid growing! The house is kept at 68 degrees in the winter and I just got a humidity monitor that says it is around 28-30%.

Anyway, I have 3 orchids right now - an oncidium sherry baby I've had for almost 2.5 years that I split into 3 pots about a year ago (bad idea); also it never reflowered...an oncidium tahoma glacier green I've had for about a year, and a Lycaste I've had about a month-which is doing well.

The oncidiums came from the same orchid greenhouse, in bloom, potted in sphagnum moss. My husband buys them for me and doesn't check the roots so both had kind of rotten-y moss that I repotted pretty soon after flowering into a bark/perlite/charcoal mix. This did not do so well - the pseudobulbs withered, leaves yellowed, and mold/mushrooms(!) grew in the pot after I tried to be more diligent with watering. I think this is because of my poor air circulation. At the time I thought my house must be too humid too, so I did some research and decided to try LECA for both oncidiums about 9 months ago (also when I split the sherry baby). When I repotted the roots were in bad shape.

At first, both oncidiums seemed to love their new media. Lots of healthy new roots and new growth popped up pretty quickly. I use the skewer method to know when to water. Over time, though, the new pseudobulbs and leaves keep growing in all wrinkly. Last month, one of the sherry baby plants dropped a bunch of leaves and a couple of pseudobulbs died, so I repotted it and cut off the dead growth. It seems to be ok again...

My most healthy sherry baby has taken a turn for the worse though, and over the last couple of days several leaves have turned yellow and older pseudobulbs turned brown. I haven't done anything different than normal and haven't repotted it since last May.

The Tahoma has never been as healthy since I got it, and it has been slowly struggling as well.

HELP! What can I do to improve the health of my oncidiums? I am going to move them all to the sunniest/warmest (probably 70-ish) room in the house, get a fan, and do humidity trays. Should I repot and cut off the dead growth? use different media?

Photos are attached - first 3 are of the sherry baby that was healthiest but deteriorated this week. next one is the sherry baby i had to cut off dead growth and repot a month or two ago, and the last two are the Tahoma that has always been a little unhappy...

TIA!