Yellow / Brown spots on leaves

Amnesia Haze auto flower at 8 weeks old. I put it in FFOF 4 gal pot. Current nutrients begun at close to 5 weeks old which was a 30% dose of FF Trio. Water maintained at 6.4 - 6.6 pH. MarsHydro TSL 2000 at 18 inches height. 2X4 tent with filter. Fans on low speed. Temp/hum run around 75-77 F with 50% RH. It looks like “septoria.” Spots form on new leaves after “a while.” Growing two plants; the other does not have it.

This is the same plant under much brighter light for clarity.

Observations/recommendations…thank you.

Looks like nute burn. Autos are nute sensitive and need even less nutrients than photos do.

Do you know your pH and PPM?

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I tried cutting back to about 20% on nutes…may be too late. pH going in will be pretty consistent 6.5 after nutes added. Have to do PPM runoff test later. Question…my water is 7.4 pH, I ordered but do not have pH down yet. Would PPM runoff test need to be at 6.5? I forgot to mention that I also add Cal/Mag to watering solution. .75ml to three pints water which equates to 1.0 to half gallon. Cal/Mag instructions indicate 1-2 ml per gallon. Too much on Cal/Mag?

Yes, runoff PPM should be in the range of 6.2 - 6.8. If you’ve been feeding it is likely that what is coming out (runoff) is significantly lower than that going in due to salt buildup. Maintaining proper runoff pH and PPM is very important for having a productive plant.

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How do I balance run off? “Flush?”

Depends how bad it is. If it is way off, then yes, a flush would be necessarily. Fox Farm soils generally go back to 6.5 after a good flush, though a flush will run your PPM way down. When I flush I use a couple of gallons of RO water with Sledgehammer and then follow that with 6 or 8 gallon of just RO water to also flush out the remaining Sledgehammer. I run 10-gal pots. If you run smaller pots then less flush will be necessary. It isn’t necessary to pH RO or distilled water going in unless you’ve added nutes to it. I always follow a flush with a gallon of RO with light nutes since PPM levels will be run down. Begin feeding normally (at low levels) on the next watering after the soil has dried out.

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This is the other plant, doing fine, same seeds. Same feeding regimen. Just strange.

Thanks for feedback; heading out to work.

It’s normal for plants’ to respond in a varied way to nute levels. They both look overfed.

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