Yellow/Browning, Don't think its NUTE burn

Set-up 250 MH lamp
PPM 650 with Fox Farms Grow Big
PH 5.5

My plants are 4 weeks into veg'ing and this one has a little bit of browning/yellowing at the top. The leaves don't feel as moist, they feel dry-like but they aren't cracking like a dead leaf would. I burned the leaves a little bit during week 2, but I've since recovered. This doesn't look like nute burn, but I'm not an expert this is my first grow. Is the PPM a little high for week 4? Or perhaps its not high enough?

Thanks for the help in advance.

Is everyone taking a break on the weekend?

Looks like the beginning of nute burn tips of leaves look burnt from to many nutes. I would flush with ph,d water and wait a week before you add nutes try 500ppm and work up.

I just looked at them. It looks like darker black/brown spots are starting to appear. I guess I was too optimistic with 650. It seems to be only affecting this one strain right now, the rest seem to be doing just fine. But I'm gonna flush and see if that helps.