Not answering your question, just a note: "lamp height around 30-35 cm" doesn't say anything at all, what is your PPFD?
Burnt tips could be due to heat stress, light stress, over feeding...
Curling down leaves could de due to Nitrogen toxicity or simply overwatering .. and so on
Yellow spots on one leaf could be magnesium deficiency..
Bottom line - you gave too little initial info to make any educated guess about issues you plant is facing