MAD Opium

High temps and a bit too low humidity during and/or overdrying, aka you water a bit too late, when plants needed it few hours or so ago, 70cm box and you have 300W light, that can make damage 4sure. There is no Nitrogen toxicity here, people are colour blind if they say so. I would say your plants are a bit pale even, would raise N part 10-20% if i was you. Still nothing major , but watering should be more frequent and with run off, collect it always, dont let plants stand in it. 20 liters pots needs around 2.5-3.5 liters to saturate it completely. divide total amount into 4-5 even parts, give 5-10 min interval between puting those parts, as mentioned before - collect and throw out run off. Slava Ukraini !!!