Burn or deficiency

Plants are roughly 6 weeks old.
Natures living soil mixed w pro mix.
spring water.

First try with “super soil”. I believe I’ve been dealing w a toxicity most of the grow but over the last 2 days I’ve noticed some rustiness on some lower leaves and some odd curling.
I do have a small fungus gnat problem but since I covered the soil with rocks they seem to be mostly gone.
What do yall think??

Temps have gone slightly above 85* F at the peak of the day

@Budzbuddha @curious2garden @Delps8 @Fishmon @Tolerance Break

I’m gonna say PH swing. This causes leaf twist but environmental stress and deficiency can be a reason too.
Not sure about “ spring water “ use.Natures living soil seems like a boutique blend of nutrients and may not be enough for plant - ph buffers etc.

This is my 2 ¢ - what I would do if it was mine.

Bag of FFOF - ADD 2-3 cups to top soil - water in with TAP water.
Just like a house plant. It is nute charged and also ph buffered.
No need for special water. Just Tap water just like you would use on any common plant.

Some bottled water can run all over the place in PH.

That natures living blend seems a bit pricey for 1lb.

If you can find this - try it .
2 tablespoons worked in and water.
easy peasy.

Looks similar to an issue ive had in the past, Where my girls had abundant Calcium available but were Calcium Deficient because they locked it out on account of an abundance in Phosphorus and Nitogen throwing everything out of balance. The temps probably dont have much to do with it unless theyre swinging from 85° to 45-50° in 24 hours. Heat stress usually makes itself known on the new growth first, and it looks like most of nastys are on the old growth. I probably sound like a robot, but before adding any nutes i would give them a good flush of maybe 1 gal of water to 1gal of container size. It wont cost you anything and is less likely to increase or do any damage then juicing up the soil. The problem is easier to solve without adding additional NPK variables to the equation. You're soil is probably excellent, but maybe a little too hot for your strain. Run 3 gals of water through (those look like 3 gal bags), let the soil dry out over the next 2-3 days and ill bet dollars to donuts she'll perk up nice and pretty without adding anything but a shower. If im right, youll notice a difference in 24-36 hours.
If you dont see a noticeable improvement in 48 hours, i might supplement some phosphorus but I doubt youll have to do that.