Yellow leafs

I was feeding the since ~ 10 days with BioBizz Fish mix with should have enough NPK for the first veg weeks. But I know that the organic feeding need more time to play out, because I just began too late with that.

Your pH is fine.... the plants were root bound and probably are again... even in the bigger pots. If you want to see what happens with weed roots, go to my diary here and look at the video I put up. I grow in DWC so there is no soil at all... and you can easily see the amount of roots that were there on that plant in a 5 gallon bucket on Day 45 or so - and she was severely stunted by my terrible treatment of her at the beginning of her life (I was learning DWC and making a LOT of mistakes). This is a link to that week in my diary: growdiaries.com/diaries/152783-grow-journal-by-growinggrannie/week/857360 But more importantly here, I don't see that you're actually feeding your plants anything? They need a good NPK regimen - the yellowing is most likely due to needing nitrogen for good growth. If the plant was older and you'd been giving it good NPK nutes, I would tell you she was starting a calcium deficiency but I don't think that is the case here... you just need to feed her. Good luck...

Really hard to answer with no information at all my guy. It is either light is too strong. Ph issue, possible soil issue but I figure not likely. Test run off pH. You should be getting good run off on each feeding. Testing that for pH and ppm can tell you a lot on grow.