Anyone have any idea what this could be?

strain is forum stomper (Autoflower) from Mephisto genetics about 3-4 weeks old from seed in a rdwc setup using AN ph perfect line currently at 50% strength along with calmag and hydrogaurd (about 8-900ppm) ph is 5.8-6.1 day temps 88-90 (constant 1500ppm c02) night temps 75-80. Humidity is 60-75%. Noticed the spots a couple weeks ago when ppm was about 300 and humidity was low around 30-40%. Humidity is fixed so I can only assume it’s a nute issue?

Have you checked the backsides of the leaves?

Heat brings pest , it looks like mites

I’ve inspected leaves with 20x scope and no pests. Backside of leaves look fine but the older brown spots eventually bleed through to the back, kind of yellowish

Mikenike said:

I’ve inspected leaves with 20x scope and no pests. Backside of leaves look fine but the older brown spots eventually bleed through to the back, kind of yellowish

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I would say for sure Calcium Deficiency, thats why your leafs are browning with spots, How much are you feeding and how often Looks like you may have too much heat, but that could of been from your humidity problem. It needs more Calcium im pretty sure.

Why are posting multiple threads on this?

I have a 9 gal rdwc and currently am at 35ml of calmag for the 9gal of water. I was thinking it was some calmag problem and have given it a foliar feed of calmag once or twice so far. Once every 3-5 days. I have a double grape plant from Mephisto as well that was showing spots and leaves started to canoe a bit. The foliar feed fixed that one right up but the one pictured above (forum stomper) is still having issues

Mikenike said:

I have a 9 gal rdwc and currently am at 35ml of calmag for the 9gal of water. I was thinking it was some calmag problem and have given it a foliar feed of calmag once or twice so far. Once every 3-5 days. I have a double grape plant from Mephisto as well that was showing spots and leaves started to canoe a bit. The foliar feed fixed that one right up but the one pictured above (forum stomper) is still having issues

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Give it more Calcium bro, if the foiler looks to be helping then that confirms the problem, Make sure you completly fix this before flipping, if its 2 weeks since you noticed it, it probably been suffering a week before that and not showing the symptoms, so like 80% of her life she has been stressed without the corret cal,mag,iron, feed more and post back after a couple feeds with results, you should see no new "spots" on new growth.

Okay so I lowered my ppm to about 720 from the high 800s while upping my calmag to about 66% from 50% and continuing a foliar feed. Plants looking much better no new spots and all leaves looking happy. I think being an Autoflower and in dwc my ppm was too high for the forum stomper. Post updated pics later thanks for all the feedback tho!