Crown rot or old age?

[Edwin Reffell]

Though my white Phaleonopsis is thriving and has last week developed 3 new buds it has a leaf which is going yellow. I have let it stand in water a few minutes to soak up water and get heavy as it stands on a table near a window facing south with brilliant sunshine several hours a day. Now I am afraid it may have got crown/root rot as a result. How do I know if it is natural aging or root rot? From now on I am going to pour water over the bark mixture taking care not to let any get to the base of the plant and let it all run through as in nature the orchid never stands in water but gets rained on and all the rain runs off immediately.