My BIKE

Hi, Can anyone please help me, I don't know if this is a fungi/disease or a nutrient deficiency. I have good ventilation, humidity is almost constant at 65% and temperature never go below 20 Celsius and never go higher than 29 Celsius. I give them special cannabis feed (bio-grow) powder. PH is 6,7 (soil). I have four plants which two are effected and the other two is doing perfectly fine and they all get the same nutrients and have the same soil mixture. Your help is appreciated.