With the issues you keep getting and with you using mainly Coco in your mix I recommend flushing the plants for a few days at a PH level of 5.8 - 6
When you do start to give them food give the medium a very light watering with Just PH water and calmag before you give them there food, COCO tends to steal the calmag not leaving enough for the plants to take so by dampening the water with a cal mag feed first allows your plant to get the full dose from your feed. (Its hard for them to Overdose on Calmag so your safe)
You say your using strips to test Ph I recommend getting yourself a soil and water PH meter, you can pick a pack that contains both from amazon for arround £25.
Try adding some Co2 into the room and my checking drainage holes are big enough that may also help + with you running LED try bump up the Temps to arround 26-28°C as they dont produce slot of heat and you want the leaf surface area to be arround 24°C other than that it looks great
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