Please help! What are these red spots on my autos?!?

Rust fungus? Nutrient deficiency? What’s happening here?? Only one out of five plants is showing this problem. A couple leaves on one other plant are slightly yellow, but that’s the only other issue so far.

I’m using kindsoil water only method. These plants sprouted Aug 16 (about 7-8 weeks old now). Water about 4.5 cups every 3 days or so. PH my water to 6.5 as recommended on kindsoil website. I have added nothing else, ever.

Gorilla Glue auto seeds bought here at i love growing marijuana.

Coco-loco on top of kindsoil bottom layer. 5 gal fabric pots.

Using blackdog phytomax 400, approx 21” above canopy. 3x3x7 gorilla tent. AC infinity cloudline ventilation. Temps kept at around 70 Fahrenheit, humidity approx 45-50%. lights on 24 hrs. no CO2 supplement.

I ordered some lactic acid bacteria serum from Redbud Soil, it’ll be here tomorrow, think that’ll help?

here’s a couple better pictures, both are of the same plant.

This is the other plant in the back with a bit of yellowing.

Looks like a calcium deficiency. Have you giving her any Cal-mag? I give mine 5ml per gallon on water only days.

Thank you for that idea Deepsix, I’m going to try that. Kindsoil website is so adamant that only filtered water should be used, I was scared to add anything at all.

I also have ordered some lactic acid bacteria serum, it’s in the mail will be here soon. Do you think it will be ok to add both cal mag and LAB serum at the same time? Or would it be better to water each in separately on different days?

Have never used the LAB serum so I have no idea.