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At first glance, I would also go for potassium, but it's hard to say. Check your pH level, make sure to increase potassium, and pay attention to the humidity in the room.

Potassium (k) deficiency i'd wager. Typicalyl when it buirns all around the serated tips like that it is K-related. P can also do this with a toxicity, though. You can distinguis betwen the two because the K-deficiency also comes with some chlorosis. get a leaf symptom chart. It seems intimidating at first, but looking at it repeatedly and comparing to plant creates familiarity over time. The good ones also explain the difference between mobile and immobile and why you see those start in certain locations ... just one more way to discern between symptoms. Diagnosing is always some portion a guess. there's lots of overlap and some are less distinctive than others. In this case i'm 99% certain it's K-deficiency. This is one of the easier ones to identify.