Leaf spots and slight fading on one of the leaves.

Leaf spots and slight fading the fading is a bad photo will take another when I get off work. I am running 1000 watt hps 20/4 light cycle they are 28 days old sour crack auto. I am running the 6/9 nute formula feeding 1 min every 6 hours. I started feeding them full strength late so don't know if these are minor causes of them being under fed or if it's a different problem any help or suggestions are appreciated. I am a new grower so I may be over worried.

The only plant to seem to have it but hasn't slowed growth from what I can tell