Lower leaves yellowing, what is required?

Hello again!

I have problems - again - with my first grow. 5 weeks into veg, the lower leaves of the plant have started going yellow. I did not use nutes, and read that this is basically a full NPK deficiency. So I applied some, namely B'cuzz aarde (two bottles, one A and one B to be combined and diluted in water. 21-14-28) . 5 ml of each per litre of water, watered, leaves still yellow. HPS light, plenty of ventilation, good temperature, and pH at approx 7. Plants currently on 18/6.

Any ideas? Should I up the nutes over the required dosage? Picture added for reference ;]

Thanks in advance!
I just hope the next grow will go over better :rolleyes:

That plant looks fine! As time goes along, those bottom leaves are going to yellow and fall off. Just introduce the ferts slowly. 1/4 strength every other watering and sloooowly increase as she grooowws!

The yellow leaves aren't going to change back to green. They're too far gone and will just drop.

Mine do that all the time. Ha haha. People here always say to introduce the plant to the nutes by giving it 1/4 strength of what is recommended on the bottle.

Okay then, thanks a lot! :)