It looks like it was really fried on that hot day.I'd take it out of the full sun for awhile,not complete shade,kind of dappled light if possible and gradually give more light. What's the potting mix? Brady

I'd live with the curling just fine, the burning of leaves is my problem, because they fell afterwards. You can see the top 2 pics and how the green color is turning to black. I'm almost pretty sure now it's spiders. We have plenty of them here, and I've crashed at least 5 tiny ones today, I've found them hanging from the leaves with their strings or whatever that thing is called. I've used all sorts of soil. Sandy one and I mean just sand taken from clean sand-dunes, sand plus potting soil, pure Ukrainian potting soil alone, and sand plus clay plus potting soil...etc I've started to give them an organic fertilizer and spray them with a pack of minerals. At the beginning I made their pots drench with water just to fill in any air in the soil, as I used to do with the citrus seedlings, but it seemed that it was a huge mistake. So far everything is in pots and not in the ground, because I live in an apartment, and the piece of land to be a little farm for my experiments is still a barren land and has no wind cover, which will be deadly during the summer and the coming autumn. The temp hits 45-48ðC in the summer, and 12-18ðC in winter. At night in winter it drops to 0ðC sometimes but not for long, and if it's a barren land than a -2ðC has been recorded. Also, winter is really dry here, and even the summer of the last couple of years had been dry as well. The pots right now are in the shaded balcony, and the temp there is around 27ðC, and I don't think they're hardened enough to be fully exposed to our harsh weather. Looking forward to hear from you and your experience.

I'm sure others with more knowledge will chime in, but you might try watering with a 1/4tsp/gallon FP solution at every watering in stead of the intermittent and stronger dosage you're using? I understand that at higher concentrations the ferts are less easily absorbed by plants, and that more dilute and frequent fertilizer applications are ideal.

Looks like a root rot problem. But A) we can't see the entire plant and B) we have no way to check the soil.