You will be happy to own that Loupe, make sure you check all around, Underside the leaves, cut a Leaf off inspect it in good ligh, triple check for bugs. If you think you've come down to a deficiency you top dress some new soil on top of your old soil, to help.ultimately if you're not using a reputable soil or super soil you might want to invest in some liquid fertilizer like Fox Farm Big Bloom.
Good luck.