Callieanthe losing leaves, dying. Beginner in need of help
 

Hello. I've had this large plant since last valentines.
Since then it has been dropping leaves at an increasing pace and I'm quite concerned. Originally i believed this to be from root rot so about a week ago I repotted it into a special potting mix for its type from the highly compacted sphagnum. It's in about a 10' pot and I don't currently have a larger one to transplant it to. It gets watered once about every two ish weeks and is closest to a south facing window. The house temp sits between 65-70 and the humidity is typically above 30%.
Some pseudobulbs look alright if a bit pruned, while others have totally yellowed and died. I'm quite upset to have such a large plant grow weak in my care, so I really hope someone has solid advice for me so l can keep this beauty. Thank you very much for taking the time to read and respond to this post. I will happily provide more photos if requested.

Welcome to the Orchid Board!

Yes, photos will help.

Your plant is probably not getting enough water. That may be from you not watering enough, or it may be because the root system is poor. Orchid roots need lots of air around them. Suffocation is the commonest cause of root loss.

Catts. in sphagnum moss need to be watered so the moss doesn't stay soggy wet. That will suffocate roots.

The time to repot is when new roots are just forming. Repotting in between can damage old roots and the plant may not be able to take up enough water until the next period of root growth, which might be months. I never cut off old roots when repotting. It's usually not possible to tell what is alive or dead.

If you plant is in a bark mixture, watering every 2 weeks is probably not often enough.