Can anyone help?? Pics included

Hi guys, I am currently growing an autoflower 4 weeks old today from seed. It is an ak 47 strain. I am starting to get rust marks on the leaves. I am using soil Biobizz light mix and feeding with 7.2 ph water and the runoff is coming out at 5.9ph. the lights are cfl, one 250w 2700k, one 20w 2700k and 2 35w 6400k with an oscillating fan all the time on the plant. I also have 2 pc exhaust fans (one is 120mm and the other is 90mm) taking air out of the growroom and 2 holes in the bottom of the growroom for intake. All has been going well until yesterday when I noticed the rust marks and today it has gotten worse. If someone has an answer for the rust issue I would love to hear from them what the cause could be. It's no real biggie tho because it's my second grow and I can crack another seed if need be.

Thanks in advance.

what type of soil are you using? I usally dont feed my autos until they are at least 4-6 weeks.

cheers for the reply, I am using Biobizz light mix.

oh ok i see u already said that....thought that was fert, sry man, not fimalar with bio bizz..... here are couple links that have saved my ass so many times its not even funny!! it gets indepth about deff. lock out and ph problems. here ya go bud!!
https://www.icmag.com/ic/showthread.php?t=231387 https://www.icmag.com/ic/showthread.php?t=11688 should find some answers there!!

it looks to me like a light nute burn....can you take a pic of the full plant?

Yea sure, no problem

it looks burnt as the bottom leaves are good, only the top appear damaged, how close are you to the light bulbs?

bulb is about 6-8 inches away from top of plant also my temp is between 74f-78f.

I'm not familiar with large CFL, but my gut feeling says the light bulb is too close

cheers, i will move it up another inch or 2 and see how that goes, I watered it earlier with 6.4 water and the runoff came out at 5.9. I'll let it ride for another few days and see how she goes and if it gets worse ill cut it and crack another seed.