Yellowish/rust colored spots - can’t figure this out.

I have two plants, one Zkittlez one GelatOG. Zkittlez is most effected.

Its week 6 and has pistils all over, likely in the middle or near the end of stretch.

It’s indoor in a 2x4 tent (8sqft)

Medium is coco in 3 gallon smart pots (Royal Gold Tupur - which is coco fiber, aged forest materials, perlite, basalt)

I’ve mostly watered them from a 15 gal reservoir with drip stakes handwatering every 3-4 days to make sure everything gets saturated.

My light is the 250 watt Series 2+ Red Spec LED from BudgetLED and it’s dimmed to about 80% until flower start. It’s right at 16-18” above the canopy.

My temps run steady at 75-77°F and my humidity runs a bit low at around high 40s/low 50s.

Ive used the microscope and no signs of any pests.



Watering schedule:

I water twice a day with the Lucas formula modified for coco (H3ad’s formula) although at a lower dosage, same ratio. Mixed into RO water. I water around 1/2 gallon each time (10-20% runoff).



0.5ml/gal Stout MSA (mono silicic acid)

1-2ml/gal CalMag (2% N, 3.5% Ca, 1% Mg, 0.1% Iron)

3ml/gal GH FloraMicro

4.5ml/gal GH FloraBloom



I ph to 5.8-6.0, mostly close to 5.8.

EC 0.6-0.8 and 500-600ppm.

Since I noticed the issues I’ve only been handwatering and not using the res and drippers.

Also looked up rust fungus and it doesn’t seem to be the issue. Looked at the spot under the microscope and don’t see any spores and when I rub the spot it doesn’t come off onto my fingers.

Bump

it's probably a bit of ph instability I wouldn't worry about the odd leaf discoloration unless it's spreading consistently...yheyl be fine...youll never see all your leaves without some problem...just keep everything balanced and it should iron itself out

maybe a bit calcium deficient? just guessing, it's nothing serious anyways, plant looks quite healty. She is not "praying" hard like some strains do, maybe is just because you took the pic around the edges of the light cylce... if not, i'll suggest checking VPD and light distance. it can be because of your low humidity and light being too close, i'll suggest getting RH to 60% vegging with these temps.. and maybe getting the light a bit more distant from the canopy, if then she stretches you just bump up light potency but try to keep it at least 18" from the tops.
for Coco, ideal pH in should be 5.5 to 5.8 for veg and 5.7 to 6 for flower. medium should always be between 5.6 and 6.4, and fluctuating it between these values in different days helps the plant uptake all the nutrients.
Hope to have been helpful!

from the plant looking, i'll suggest even a light defoliation on the big fan leaves shading tops