Brownish Lower Leaves

These are a mix of OC, AK48, and White Rhino. The grow is under a 400w HPS light and I am giving them FoxFarm Nutes and growing them in FoxFarm Soil. It is about a month into the grow, I did them 12/12 from seed and they have brownish lower leaves and they pretty much just die off really quickly.

I know it is a little warmer than should be but should that really affect the leaves like this?

Any ideas?

Im using fox farm soil, and tiger bloom, and mine are doing something very similar. I just picked up some cal-mag plus today, and I hope that fixes it. It looks like a magnesium deficiency i think.

do a flush i suspect salt buildup