What is yellowing my little leave ?

That is classic sign of nutrient burn . You're feeding your plant nutrient water too often . One thing you gotta remember is that soil tends to retain nutrients alot better then well say hydroponics set up or soiless mixes . You're going to want to stop feeding her nutrient water until the yellow slows then comes to a stop all together . When you decide to start using your nutrient solution again start with 1/4 strength and work the doses up as the plant gets older . You might also want to remember that the damages you see on top (your leaves) will be the same damages in your root zone . Over all your in good shape just got a few minor things to correct and you will be rocking and rolling , you could even get a rooting agent and a chelation agent (Voodoo juice , B52 only examples) to help your plant recover faster and grow stronger . Products like voodoo juice enable your root mass to get huggggeeee and uptake more nutrients and products like B52 are like protein shakes for your plants muscles it will help rebuild faster and stronger ! You don't have to get products like this but there are a wide variety of them so if you choose to go that route make sure to do your research first . I hope you find this information useful in your quest to becoming a master grower ! -Happy Growing!