First grow-possible issue

Hello all. I'm currently in my first grow, its blue mammoth from Barneys farm. Its 15 days old, under a 100w daylight cfl. So far, I haven't given it any type of nutes. Its growing in Happy Frog (only getting nutes that are in the soil). The largest leaves are starting to turn yellow very slowly. Just getting a yellow hue to them. I'm considering adding in Big Bloom. On the largest leaves....there is just a tiny little rust dot on both leaves. Just one spot on each the size of a ball on a ball point pen. Other than that....its growing at a decent pace and appears very healthy. I just want to nip this in the butt before it gets worse.
Ps. How do you load Pics from mobile?

You might be overwatering, and you could definitely do with more light regardless...since lack of light will cause yellowing too.

It's very unlikely that you're out of nutes from happy frog in only 15 days!!

Thanks for the reply. I'll bump the lumens up. I failed to mention my temp is at 82 degrees. Guy at hydro shop said this high of a temp will cause less nutrient uptake...possible nitrogen deficiency. I'm gonna try to get the temp down a bit. I'll bump the lumens up too.