Isabelia virginalis leaves yellowing and falling off

[Mikefromearth]

Hi all,

My Isabelia virginalis doesnt seem very happy. It's continuously growing new leaves, but the older ones keep turning yellow and falling off.

It's mounted on a stump in my terrarium up near the light. I water it every 2-4 days, mostly in the morning, and it dries by night time.

The environment is very humid, I would say 80-95% humidity. There is no air movement right now other than me opening the lid and blowing air in manually.

I have never fertilized the plant.

I assumed in the beginning the problem was over watering or too much moss holding too much moisture around the bulbs, so I removed 50% of the moss and started watering it less, but the problem persists.

Do any of you have ideas as to why the plant isnt doing well? If so, please help!

Thanks!