Hello ! Well you're growing in coco then your ph range should be between 5.8 and 6.3 and 6.5 is the maximum , what I can see is a slight ph burnt to me. You should low a bit your ph and check the runoff ph as it can be deifferent from the input ph so it's the best way to correct a fluctuation in coco. I hope it will help you 😁👍