Brown/Rusty spots on leaves after dark period

THraCian

New Member
I spotted some brown/rusty spots on some of my plants leaves after their dark period. Before lights out I didn't spot any of them, humidity was up quite a lot about 70%, because it's raining and I still don't have a dehumidifier, but not sure if that's the issue. They are 22 days old (since seed in ground), about 15 days from sprout. I am using BioTabs Just add water strategy and BioBizz LightMix with some Perlite added for medium. I only water once the top 3cm(about an inch) of the soil is dry.

From my research it looks like a Calcium deficiency, but this is my first grow ever and I am not experienced enough to recognise it correctly.

Any ideas what might cause this?
 

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