Brown spots/tips on lower leaves

Hi all,

been reading these fourms for awhile now and they have helped me set up my first grow.

I've done a search and have found nothing that really answers my questions. Right now I have two plants about 2" tall (about 2 weeks old) that are developing a mass of brown spots on their lower leaves. They also have brown tips on the first set of leaves it grew. I'm running a DWC system. Stats are:

PPM: ~500
pH: ~6.5 (too high perhaps?)
Temp: ~76F

As per the Fox Farm Hydro nute instructions, I've added some Grow Big and just a bit of the Big Bloom. Up until a few days ago I was having bad heat issues. They have been blasted a few times with ~90F heat. They lived the first week and half of life around ~85F. I've now got that under control. Could I have stressed em out with the heat issue? I've included a few pics so you can see the damage.

Anyone have any idea what is wrong with my babies?

im no hydro grower first off. but i would say if your short any thing its potasium. the first pic kinda looks like nute burn or possible K def., when added with the brown spots. i suggest you get more opinions from hydro growers though before doing too much.

Anyone? Really could use some help. Leaves are getting worse.