Looks Like Rust Spots??

Not sure what it is? In about week four of flower, any ideas? I use an RO, I add cal mag, big bud, carbo load, and an all purpose. Thanks

Looks like.Boron. But it is not absorbed will without enough potassium and nitrogen, or if there isn't enough moisture. Your plant may also exhibit signs of a boron deficiency if the pH is too high or low. Flush your system with clean, pH'd water that contains about half the nutrients needed for the plant and watch to make sure that the problem clears up for new growth.