yellow brown rusty spots HELP PLEASE

first time grow, i have a 600 hps in black gold soil good air flow. temp 72 during day and 60 at night, hum 40%. i'm using purvida organic grow and bloom. no visable bugs on the plant at all. ph is 6.5 help please PLEASE

Dolomite? You have a cal/mag thing starting. Check for spider mites too. You will need a scope. Likely the cal/mag thing.

do you check your run off water ph? looks like it might be off.