Infected catt

[MrHungx]

My C. Portia var. coerulea 'Mrs. Carl Holmes' HCC/AOS shows signs of an infection (possibly black rot). The plant initially appeared healthy until I set it outside in the afternoon sun. Before I bring it inside for the night, I notice black splotches on the leaves. Fearing black rot, I cut off the infected parts using a sterilized knife and spray the entire plant with Physan 20. The day after, I set the plant outside. I check on it later and more of the plant has turned black (it wasn't there when I set it outside)! I'm beginning to fear that the entire plant is infected and I have emailed the vendor (Hausermann's orchids) as this was a recent acquisition. I have been treating my orchids with calcium/magnesium supplements (thanks Silken!) so I know it's not an infection due to nutrient deficiencies. So is this infection black rot?