Help identifying brown spot issues

Hey there. This autoflower is currently at week 6. I started it about two weeks ahead of my main 4 plants to use it as a test plant to try and figure out the feeding schedule and the soil itself. Figured if I ran into issues a couple weeks ahead of my others, I could maybe be more proactive.

It’s in FFOF with 35% perlite and dolomite lime. Around week 4 it started to show nutrient decencies and I fed it a half dose of Grow Big and Big Bloom with 3.5ml of CalMag all into a gallon of dechlorinated tap. PH for the feedings and waterings have been between 6.4-6.6. My soil ph is currently at 6.3. Average temps are 79-82f with 45-55% RH.

After this feeding, the next watering was plain water at 6.5ph. All my waterings I water to about 10-15% run off.

The rust spots started about 4-5 days ago, yesterday was water day for it, so I gave it another half dose of the above mentioned FF nutrients, with the same amount CalMag. They spots to be increasing but I’m waiting another couple days to compare it to a photo I took yesterday.

Am I right to think that this is possibly a deficiency with cal/mag?

How are you reading ph? Double check the run off bc something tells me it's off. Cal mag issues go from bottom up so I'm assuming you've already lost the lower leaves.
The other leaves look super green so try increasing the cal mag and leaving out the feed next watering.
What size is the pot?

@Greenthumblady thanks for the reply. I have a digital soil ph meter along with a calibrated water ph meter. Run off is around 6.8-7ph and I’m usually watering in around 6.5ph. I’ve assumed this run off ph is bumped up due to the dolomite lime buffer. I’ve been told that a .5 or so difference in run off ph doesn’t matter.

Its in a 1 gallon container. The lower leafs are not yellowed and are still there. They have no signs of this brown spot issue the top leaves are showing.

It's hard to tell the size of the plant. More pictures please.

What kind of digital soil meter?

My next guess would be possible phosphorus deficiency.

Greenthumblady said:

How are you reading ph? Double check the run off bc something tells me it's off. Cal mag issues go from bottom up so I'm assuming you've already lost the lower leaves.
The other leaves look super green so try increasing the cal mag and leaving out the feed next watering.
What size is the pot?

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I was thinking Magnesium also, and/or potassium.

Sorry to jump tho post I'm not getting any help from other parts of the site. You guys seem to be very helpful on this post. I have this issue. Growing in soil biobizz. pH is at 6.2 using bac bloom /pk booster/bloom stimulator. Running led spider farmer sf2000 X2. I have tried using calmag but still not letting off. If any one can help that would be great I am about week 3 in bloom with ww. Thanks

kylewright201 said:

Sorry to jump tho post I'm not getting any help from other parts of the site. You guys seem to be very helpful on this post. I have this issue. Growing in soil biobizz. pH is at 6.2 using bac bloom /pk booster/bloom stimulator. Running led spider farmer sf2000 X2. I have tried using calmag but still not letting off. If any one can help that would be great I am about week 3 in bloom with ww. Thanks

Click to expand...

Looks like potassium deficiency to me.