Help - Yellowing up top

[Rifleman]

My big girl BK has started to show some yellowing in her top leaves. Her PH has been a little low this week, 5.6-5.7. It's only on the larger leaves in the top 25% of the plant. I'm thinking maybe a copper def since I'm not sure which PH range it gets locked out and it's on the upper leaves. Any suggestion, tips, or criticisms? ?

 

[Rifleman]

Re: Help w/ yellowing up top

No guesses huh? No problem, I believe that I have it figured out. It's a Mg def caused by my low PH. Why is it showing in the upper half of the plant you ask? Because those are the largest and busiest leaves fueling the intense growth. Another reason why I let my girls go natural. I know some who defol at this point to increase bud size, but I think it is detrimental. I might be incorrect, but I'm betting an increase in my PH will fix this.

 

[BuddroGreen]

Looks like the starting of Mag, I think you're on the right track.

 

[Major PITA]

I suck at this kind of thing, but my guess leans more to manganese than magnesium.
Why? I believe magnesium is more likely to hit medium-older leaves first even though it is a mobile nutrient. I also don't see the usual evidence of tacoing leaves. On the other hand, manganese can look a lot like the same problem but hits top leaves first. Dunno - just throwing it out there...

 

[Ripples]

Looks like a PH Fluctuation to me? You mentioned it was lower than normal... Otherwise the little lady looks fine!... Happy Growing!

 

[Thehalobluntm]

I think it's light bleaching snice only on top and makescalot of sense. Do you foil feed cause I think that helps it bleach as well being too close to lights