Leave burn or nutrient deficiency

Hi Everybody,

Need some help, can't figure this one out...

This is an indoor crop on Top-feed system
In week 5 of Vegetative Growth
400W MHB - 16/8 Lighting cycle
EC - 0.40
PH 5.8
Temperature 30°C / 83°F

The problem is only appearing on the bottom leaves but is slowly moving up the plant.

So please let me know where I'm going wrong

Thanks

Moving to the Leaves above.

that looks like rust, hows your airflow?

I have an inlet and an out let fan in my grow box, its on 24/7. Perhaps its not strong enough?

looks like magnesium deficiency, altho it could be too much damage from nutes, or ph. Get some miracle grow tomato plant food, and dilute it slightly more than recommended and try that. Its like 3 bucks at a hardware store and will last. self diagnose it with this link pulled from the FAQ. Hope it helps. https://www.rollitup.org/view.php?pg=faq&cmd=article&id=37