Candoliked comment
<span class="link_user">@Cando</span>, Thanks for your message. I think the yellowing leaves are because my PH was incorrect. I found out that my PH meter was not working properly, so i bought a new one thats a bit more expensive.
In my understanding the tips of the leaves will get burnt if there are too much nutrients in the soil.
I still give the same nutrients and they are doing very well :grin: