Hello
@mrhat2001 ! While you have perfect conditions for rust fungus development i don't believe this is rust. If you scratch the leaf, rust fungus will leave to your fingers yellowish/brownish dirt like. You can also use a small microscope like those we use to check the trichomes ( https://www.amazon.com/Forrader-Pocket-Microscope-Currency-Detector/dp/B00JEKXBQ2 ) and if its rust you should see tiny yellowish/brownish spores especially at the underside of the leaf. It might be a slight nutrient burn or a calcium toxicity but i can't tell for sure with these photos. I am talking about calcium toxicity because it has rust fungus symptoms except the brownish/yellowish dirt when scratching and i see that you use flora micro hard water. So if you have a hard water source why you give extra cal/mag ? The EC value of cal/mag alone should not going more than 0.4 ms/cm. Anyway i really believe its nothing you should worry about. Happy growing ! š