Help! yellowing and dying plant and leaves

My plant is experiencing weird symptoms, if you could please help and direct me to the solution.

all of the leaves are turning brown at the edges, and turning yellow in color at the same time.

My trouble shooting form is as follows:

This is my first grow

My Equipment:
Natural Sunlight, at this time of year 14 hours a day

Medium:
Type of soil: a fertilized peat mix mixed with a little sand (I bought it, but its composition was not written on the package)

Container: 30cm plastic pots

Germination: Germinated in cotton

Your nutrients and water:
Source of water? Using tap water, 6.8pH

Using a 4:2:2 fertilizer mix of a local brand. fertilized twice at a 14 day interval a 1/4 of the recommended dose

My growroom is outdoors, but they are placed in pots.
High temperature 75-100F and high humidity 40-70% (its an equatorial climate)

The Strain:
Skunk #1, grown from regular seeds, it is a 75% Sativa, 25% Indica mix.

There was a sudden heat wave, where temps soared to 115F. I have a feeling this is what has caused severe heat stress. I am attempting to keep them at a stable temperature. I doubt that this is nutrient burn since the intervals of the feeding are so far apart and it exhibited these symptoms after 8 days of the feeding.

Im am not very sure what's happening to them, and would much appreciate someone with more experience to help diagnose the problem, as this is my first grow.

See pix!

Thanks!