What kind of deficiency is this?

This is one of my white widows that I’ve been growing and it was just fine until almost a week ago when the leaves on top started to spot and turn a strange type of yellow and some brown, my other white widow is just fine and my other strains are as well. I don’t see any bugs or mites on or under any of the leaves. I’m assuming maybe it’s a calcium or maybe magnesium deficiency but I really have no clue. The leaves don’t really sag or anything and it hasn’t really slowed in growth either so far I can tell. If anyone recognizes or knows what it is I’d love to hear your thoughts cause I’m clueless.
check again for mites up-top, check carefully, if you don't find them (and I think you will) then you need to list everything you're feeding and doing
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