Whats lacks?

That 100% is nitrogen. When the leaf shows dark coloring along the veins like that, it is nitrogen. Calmag you would see brown somewhere. That is for sure early nitrogen deficiency.

Now the ting for me is to add some iron but Advanced Nutrients dont say nothing about It Advices about iron integration?

Looks like it could be iron. It's in the upper growth. Cheers!

He's doing real hydroponics. PH is fine to be set at 5.8 even at 5.5 And after 2 days it'll be in that range. Not PH.

Hey bro. I'm 90% there in agreement with you. It's not calmag. There's enough calmag in the sensi line. And iron strikes more so in real hydroponics earlier on. Calmag is more of a latr stage shower as there's enough calmag even in soft water for the 1st few weeks espically in hydroponics. It might also be PH swings that's locking out something. I don't have enough experience to say for sure you are right. But there's no Iron in anything that you have. Lots of cal sensi line. And again there's enough calmag in your water and in AN base nutrients.

Going to disagree with my grommie here... calmag is not needed until flowering - what's needed when they're 2 weeks old is good old NPK... but the problem you're facing is your low PH... you need to bring that up to 6.0-6.5 (6.3 being the absolute SWEET SPOT)... outside that range, lots of nutrients and micronutrients aren't going to be available to your grow - you can supply all you want but if the PH isn't right, the plant can't take it on board. So bring up your PH and happy growing! Good luck!

I noticed your not using a calmag supplement. Highly recommended using one, stick with your nutrient brands calmag. Looks like start of magnesium deficiency.