help please

[stuz]

How you doing
Nice to meet you all, first time grower looking for advice.
Set up.
120x120x200 tent
8" extract
6" external intake fed from window
400w hps magnetic ballast
Temp
79f lights on
70f lights off
Humidity 53%
Medium
Light mix soil bio biz ph'd at 6.2-6.8
11l pots kept 18" from light

Watering 3-5 days pending on dry the soil is.
Plants are big buddha cheese aged 21 days from germ.
Started on 250w cfl then progressed to 400w hps, planning on switching up to 600w hps in flower.my problem is the lower leaves have started to turn yellow and droopy and unsure why?
I'm not adding notes at the minute as only recently transplanted and led to believe that there should be enough food for them for the next few weeks with water only ph'd to 7.0

 

[Conradino23]

There might little nitrogen in your soil and that's why they're getting yellow.

 

[stuz]

 

[Conradino23]

This is phosphorus deficiency, very common in young plants which grow in a very light mix or have too high PH.

 

[stuz]

Thanks for the quick response gents I'll look into both these, iv read loads but think iv over done it n smoked my brain lol