Leaf Issue on Flowering Plant - Normal or Problem?

[MaineGreenery]

So I have three bag seed plants that are in the third week of flowering. They are watered every third day and fed fox farms nutes per ff schedule at 1/4 strength. Temps are between high 70's to mid 80's. Humidity is around 55%. I am noticing yellowing and weakening of the lowest fan leaves on all of the plants. Can anyone tell me if this is due to something I am doing wrong or if this is normal plant aging? This is my first grow and I am paranoid about everything about them. Here are some pics of the leaves and set-up.

Thanks for any thoughts you can share. More details on the grow are available in my journal in my sig.

 

[homedoggydog]

Nice looking plants. I just had the same problem. I'm no expert as I am only on my second grow. 1/4 strength may not be enough and you may have a nutrient deficiency. How is your pH? The yellowing looks like a lack of Nitrogen. Try watering with full strength nutes and see if the yellowing stops. Into flowering the soil can get stripped of nutrients.

 

[fanleaf]

Look hungry to me. A little early in flower to run out of N. Go 1/2 strength for a try.

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[improvise]

Maybe i`am wrong but this happens to me as its not happening all over the plant my theory is they are natural fall leaves away down there in the shade as the canopy gets bigger not receiving light so the leave is not working to full potential so plant then takes back all the goodness from the leave which causes the yellowing and dying just like autumn fall.
If it was all over the plant then it would be more cause for concern. Nice looking plants by the way. regards

 

[MaineGreenery]

So I fed at 1/2 strength yesterday after feeding at 1/4 strength the day before. I am hoping it is a N def. Based on other's comments and the research I have done online it does seem very likely. They are growing like mad and all that mass must need a lot of N. I did test the PH of the nutrient solution. I don't have a soil tester and testing the solution going into the soil seems a good substitute. The results came in around 6.0 - 6.5 as you can see in the pic below.

I will update in the next couple days and let you guys know if this helps clear up the issue. Thank you for your help!

 

[Bud Good]

The results came in around 6.0 - 6.5 as you can see in the pic below.

That looks pretty close to 6.0, I'd up the pH just a little. I had similar problems with low 6 pHs, moving up to 6.5-6.8 helped. I'll alternate so one feed/water is closer to 6.5 and the next closer to 6.8. I don't know that to be beneficial, but it seems to me like it would be. Doesn't seem to be hurting anything anyway.

My digital meter stopped reading correctly, and I started using the same pH test solution you are. Up the pH to where the solution has a bit of brown in it, but don't let it have any green.

And as someone else said above, it is normal for plants to suck the nutrients out of leaves that are in the shade. You might not even have anything to worry about. If it's not contributing anything to the plant, the plant uses up what's in the leaf and then drops them.