GDP Help

Have this GFP finally blooming. Grown In 3 gallon fabric pot with Walmart soil . Giving bloom booster just over the counter type. Notice my leaves looking like this just a few of them. Any suggestions?

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Looks like Mg def in the final pic - necrosis in the leaf matter but not in the veins.

Cal Mag may stop the spread.

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Might want to have a gander under the leaves with a scope too, just in case.