Leaves curling up and browning

Looks like potassium burn, sometimes the older leaves suffer first, but the younger leaves will show burn too especially at the tips.

This is burning from feeding too much or too often............or both. Cut your nutrient strength in half, with the small lighting you are using, the plants can not use all the nutrients that you have been giving them. I would be giving them just plain water for the next 7 days, before resuming with feeding at half the strength you were giving them before. This will give them a chance to use up what has already built up in in the substrate before any new nutrients are added.

If it was heat or light, the leaves affected would be the top-most leaves... This is a phosphorus deficiency probably with a calcium deficiency to boot.... Make sure your pH is in a good range (6.0-6.5)... that's usually the cause of both although a nitrogen toxicity could also do it - but I'm not seeing evidence of that... Good luck!

Hello !!!! The leaves of the plants close up to avoid dehydration or due to burns. Control the temperature of your room and the distance of the light above your plant. Good luck.