Hi, what is your PH? Clearly there is something wrong—-
It’s not uncommon for bottom leaves to die off as they get less light…. But the rust is most likely from PH. And the green you have going on looks really rich—- just based on color—- almost like too much nitrogen.
Run off numbers? If you cannot test for any of this, just feed the plant plain PHed water for a few days with run off.
Then make sure you have cal mag and the proper nutes for that cycle time