Spots on leaves and yellowing. Lower leaves. Dos si do

Hey So i think you're right with calcium being part of the problem. The spotty rusty leaves i usually associate with calcium... I think we should also think about a possible phosphorus problem also though because that and calcium are closely connected and often have problems together, especially with the red stems present. But given the nice diet you've got going on i think it might be more a problem of ph...and the nutrients are getting locked out. Are you monitoring the ph? If not i think that would be the best place to start. I know these "ph perfect " lines are a big selling point, but i don't believe they're completely accurate all the time.