What is This???

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Hi All! First post, hope you all can help. Here is the sitch:
I am growing White Window in soil with Ocean Forest and very little nutes (Grow Big). After we transferred to 3-gal bags a couple days passed and this showed up on a number of plants. It started as little square burns. All on lower leaves. This makes me think its a mobile nute that spread to the upper leaves, leaving these lower leaves deficient. A shop guy said it sounded like potassium deficiency (or lockout) and I used cal-mag a couple times. The forum sounds more like Manganese or something.
Any ideas? They are growing well but I want to learn. Thanks for the help!

Were the 3 gal bags filled with Ocean Forest also? There shouldn't be any deficiencies if so. Maybe the water is too hard / wrong pH?

it dosent look like mag def it looks like p.h but im wondering why its not really in your lower growth

sparkabowl said:

Were the 3 gal bags filled with Ocean Forest also? There shouldn't be any deficiencies if so. Maybe the water is too hard / wrong pH?

Click to expand...

I went from ocean forest in 4x4s to these bags. I've tested soil PH and it shows as 7 (if accurate I guess), and the plants are five weeks old when this happened. Growing from seeds if that's a question.

try to drop her down to 6.5

Thanks all for the advice. I checked all my plants last night, and it looks like the PH of the affected plants hovers just at 7, while the unaffected are showing 6.5ish.
Can this little bit make that much difference? Amazing yo!