4 week plant - top turned yellow

I've seen yellow tips but never the top multiple leaves turning a pale yellow. This is a 4 week NL in hydro on a Humboldt regimen of Oneness, Ginormous, Sea Cal and Sea Mag. The bottom 2/3 of the plant look good and the roots look normal. These top leaves don't seem to be drying out or even looking unhealthy, just yellow. I'll post a pic as soon as my camera battery charges.

OK here's a pic. The pic doesn't show the yellow as being even as yellow as it really is. What's weird to me is, the yellow leaves seem normal otherwise and the roots look good.

Is it possible it needs more food? What are you feeding in at?

I don't think it can be underfed. It is getting Humboldt's recommended feeding schedule and was just fed yesterday in a new res. I might worry about over-feeding except that I have long used this schedule and never seen this. I'm just wondering if it might come around itself, and if the top is still viable.

Yea sure the top is still viable see if it darkens up I know iron deficiency starts in the new growth which lacks chlorophyll but has no necrotic spots this causes them to turn bright yellow except for the viens. Kinda tricky because iron resembles a mag def but maybe look up fe def see what you think

Only reason I say iron is it effects the top where as mag starts from the bottom or middle of the plant

I have thought of iron but hate to start supplementing on a guess because sometimes that just makes things worse. But I agree it is better than a guess and I will probably try it.

More research shows that overfeeding of other elements from calcium to manganese can cause iron lockout and iron deficiency symptoms. But again, I trust Humboldt and I'm feeding their schedule. They seem to be greening up some, except for the very tops. Guess I'll wait and see.

Yea I mean leaves are perked and look nice just are a little yellow. . I guess I was just trying to help brainstorm. Glad to see your willing to stick to the line as well. You'll make it work im sure one way or the other.

Swing on the spiral Brutha!
Peace