Brown spots due to light height?

Looks to me like the start of a potassium deficiency. If it started on the lower canopy then calcium( which your not adding any cal-mag. Usually required unless you have really hard tap water. ) I rant into the same with my first grow doing a 1 grow :2 micro :3 bloom ratio for flower with general hydroponics. when it should be more like a 2:2:3(grow,micro,bloom) the Gro has a lot of potassium in it and most nitrogen comes from the micro. Stick with the feed chart for your ratio https://generalhydroponics.com/resources/flora-series-feedcharts/