if you look at the tips o the other leaves, you'll see it's present there as well, albeit not to the same extent as this one. this one actually looks fried on the very end, the other ones only yellowed slightly on the very end of the leaf.
the burnt/fried tip depicted in the photo only showed up today. I'd say it's getting worse
They look fine to me. I don't suggest feeding it anything for a while. Even though you might have fed it nearly a month ago, a nitrogen burn can be delayed because of slow-release fertilizers.
Have you thought about testing the pH of the soil?