Slipper orchid showing yellow brown at crown

[iLoveOrchids101]

Last Friday (8/25) I noticed light yellowish leaves (near crown) on Slipper orchid. I watered that orchid that day. Now today (8/28) after two days, I see that yellow brown mark has spread and become more darker. The photos show the progression. The first two photos from 8/25 and last two photos from 8/28. The only change was I used to water this Orchid once a week and this time I watered it after 4 days since the bark medium was dry. What do I need to do. Appreciate the help.