That looks like tip burn caused by excess nutrients a very common problem from giving too much nutrients in the feed or using a soil which has a lot of pre stored nutrient in it.
If you are giving it nutrients stop, normally soil should have enough feed for about 3-4 weeks. Especially bio all mix which is sting stuff. You are using 5ml per litre of feed which is way way too much at this stage.
I am using roughly half of what you are and my plants are huge.
Give them just water on your next feed and don’t water to run off as it will take that pot too long to dry.