Beginner Gardening: Dracaena (corn plant) leaves edge brown spots, 2 by kenyong

kenyong wrote:
My corn plant has been pretty healthy for the past six months and then today suddenly I saw two brown spots on one leaf (incidentally this leaf doesn't look as healthy) and darker brown spot on two another. The three leaves are relatively new leaves. I noticed the brown spots this morning so I am not sure how long they have been there. I use tap water (soft water, has been left out for 2 days to evaporate chemicals) for years and never really notice these brown spots. In addition, I changed my soil about six months ago. Also, I never fertilize the plant.

I inspected the plant and there are no insects or mites. All other leaves are fine. These three leaves are on the same stalk. Please kindly let me know what's going on and what I should do! Thanks so much!