New Dendrobium with soft brown leaf

[dendrite]

Hello! I am brand new to orchidboard and new to orchids other than good old phalaenopsis. I bought a Dendrobium around two weeks ago and have been watering it on a weekly basis (so about twice all together). One of the leaves has begun to have some sort of rot- it is brown and mushy to touch. I am not sure if this is black rot or another bacterial rot. It does not appear to extend to the stem, rather it started at the tip. Should I cut this leaf? Should I repot the orchid? The rest of the orchid looks fine to me