Need assistance with yellowing & dying leaves!

[roidetoi]

Strains - Utopia Haze, Supreme CBD Kush, Durban Poison
# of Plants - 4
Grow Type - Soil
Grow Stage - Just starting flowering
Bucket Size - 20 Gallon
Lights - Outdoor
Nutrients - Advanced Nutrients Micro, Grow, Bloom, B-52, Voodoo Juice
Medium - Commercial organic soil
PH - 7.0
RH - 25% to 40%
Room Temperature - fluctuates based on weather. We had a major hot spell (high-90's to low 100's) for over a week in early August
Pests - None

Problem: This is my first year growing, and in general, things have gone well. I started the plants indoors and moved them outdoors in early May. They grew fast and with few issues.

In July, one of the plants (one of the two Utopia Haze plants) started getting quite a few yellow leaves in the lower part of the plant. The other plants had a few, but not as many as this plant. The leaves of the plant are curling down. As the high heat that hit our area a couple of weeks ago bit, more leaves turned yellow and died.

I have been very careful to make sure the pH is correct, and I have been using the recommended nutrients every two or three waterings. I have also been careful not to under or over-water the plants.

What could be causing this problem, and why is it much worse on one of the the plants than the other three? I give them all the same nutrients and care.

Here are photos of the plant with the most problems:

 

[daTenshi]

I am no expert by no means and your plant looks great to me so take this as an opinion. Some yellowing is normal as they use the nutrients to kick off flowering. Now for the way the leaves are cupping inwards indicates low moisture to me (the rh is too low with high temps).

 

[AnimaSola]

Try insulating the roots by burying the outside of the pot to shield the roots from the heat of the sun. Those things are trees, I like adding a small amount of veg nuts to my larger flowering plants. They are using the lower leaves for food because they are N hungry or the roots are getting cooked or you have pests, hard to tell but preventative maintenance is key if you want a good harvest.

 

[Mnmmc]

Hi all
@daTenshi
Well one plant just died and now a second plant doing the same kind of thing. I flushed out once and the PH was low 4 or under.
The plant is almost 4 feet high
I used
Reused pro mix soil
Advanced nutrients mirco,grow and bloom.
Lights are 1200 watt less have one small fan circulating air and in a 5 x 5 grow tent.
Temps average about 68 to 72 degrees RH is 45%

Hope to fix this thanks anyone who can suggest or help.
Peace