Leaves are drying up and turning yellow

The problem is salt build up in your coco. Coco coir is a hydroponic medium and needs to be irrigated at least once a day, with lots of run off. Run off should be discard in Drain to Waist setup or sent back to reservoir in a Flood and drain setup. If you try to treat coco like soil letting it dry out like on the pictures it fucks your pH. If you don't water until you get 10-20% run off, because you feed every watering salts accumulate and also fuck your pH and cause lockout. Also if you got your coco from a brick it mostly needed to be rinsed and buffered with CalMag. Now on top of that, the nutrients you are using are meant for soil. There is no organic hydroponic cannabis friendly nutrient. Nutrients for soil are meant to be processed by soil while hydroponic require nutrients in salt and mineral formula to be absorbed by the plant. You will need to flush your coco. Have you ever done it? put your plant in container in your bath-shower, and dump 5 times the volume of your container in pH water. Then get some nutrients for coco, like Canna coco, General Hydroponic, ... if it is good for hydro it is good for coco. Use them at 50% of feeding start to start and see if they need more. Acting quick is the key when your plants are in a salty medium. Just like with humans, salts keeps the plants from taking up water. But after flush your soil will be depleted of every food so it crucial to feed them as well. Not ideal on Christmas day to put your hands on hydroponic nutrients... Hope this help, and if you don't know Dr Coco take a look at this awesome site cocoforcannabis.com.