B. tortuosum losing leaves
 

Was wondering if anyone can help me.
I have had a Bulb. toruosum for several months now. It has been growing well and flowering constantly. I have it mounted on cork (sphag. cushion) in a vivarium. Humidity is between 60 to 75%. Temperature is room temp. (20to 25 deg C). Also good air circulation. Just recently my plant has started to lose leaves. They just fall right of the pseudobulb. Any reason for this? I don't think it's a deciduous plant, right?

Not sure. I water once a day and the orchid does dry out between watering. I do water by submersing the whole plant under water for a minute or two.

It doesn't stay wet very long. There are no signs of rot or bacterial infection. And even the new leaves have fallen.

B. tortuosum is in the section polyblepharon and, at least IMO, those plants tend to be fairly picky about their culture. If the temps are consistent at 20-25 C, and you don't have a significant drop in temperature at night that may be part of the problem. High humidity and constant airflow are also a must, however growing in a viv your humid is most likely high. If you can increase your fresh airflow and provide slightly cooler nights that may help. Good luck.