Yellowing leaves cause?

Yellowing leaves have affected both of my plants at the base. A couple of the yellow leaves have brown spots. Anyone know the culprit?

-LEFT PLANT:
(9L pot - Westland Potting Soil)
Auto pink kush, week 6 (flowering week 2)
Had nitrogen toxicity previously but I believe it has since been cured.
-RIGHT PLANT:
(5L pot - Miracle Gro Potting Soil)
Auto Alaskan Purple, week 7 (flowering week 3)

I water roughly every 2 days and add nutes every 2nd water (so nutes are added every 4 days roughly)
I’m adding Biobizz’s biogrow and biobloom as my nutes.

specs:
MarsHydro 300w LED
2 oscillating fans, 1 exhaust, passive intake.

Humidity: 36%
Temp: 24 degrees celsius

That's a completely normal part of flowering, weed is an annual plant so when it's flowering it's also getting ready to die, it stops sending nutrients to leaves it doesn't need anymore so it can concentrate all it's energy on reproduction (bud production).