Is this due to the sun and hot weather?

looks like nutrient burn

She has signs of both P and N toxicity, unless you supplemented with a high dose of these recently, then its defenitly from underwatering (soil being too dry) more heat= more need for water.

Si estimado, que las puntas de las hojas estén enroscadas hacia arriba quiere decir que el sol está afectando negativamente ya que las plantas se intentan esconder del sol. Recomiendo mantener húmedo el sustrato para que dentro de la maceta se mantenga una temperatura "baja" y cambiarla cada ciertos momentos a la sombra durante el día.

That's over feeding, also called nutrient burn (burnt tips and edges). See how dark the leaves are? that is not normal, leaves should be light green, not dark, that's another symptom of over feeding. Stop feeding it, and give it plain water.