Hello - I have a newly purchased Lisbon Lemon plant that I purchased about a month ago, and I'm just trying to get the hang of this citrus growing thing. There have been new leaves growing on my lemon since I bought it (these new leaves in the picture), but they're also developing a crinkled dried brown area on some of them. The older leaves do not have this deformity.

To my untrained eye, it looks like fertilizer burn, but that doesn't make any sense because I haven't used any fertilizer yet. The plant is in a terra cotta pot, and I believe that it's been watered adequately (about twice a week).

Any thoughts? Thank you very much in advance!