I am also getting brown spots on leaves as well... I posted this in another section, maybe the answers we get can help?
I have included pictures of the setup / I cannot tell if it is a slight nute burn because it is the middle of the leaves on one or two that have become a light brown and spotty (only one leaf has a single browned tip on a different plant). The ppm in the solution is 191 after just measuring it and have better ventilation (no fanning was on it before or barely) which could explain the burning in the first place. Temp picture and humidity included as well (generally is in 40's with door closed.) and temp was higher in the 80's before and managed to cool it down over a few hours and different rigging. It probably is just light burn, but I am hoping for more opinions and really am not wanting to kill them since it is my first grow!!! There is a solution of flora grow series + B vitamin and they all 1/4 of the normal seedling dosage per gallon (w/ exception to the B vitamin which recieved 1/2 normal dose per gallon)... HELLPPPPP!!!
(update, temp is now down to 70-75 and added a half gallon more water to dilute the nutrient solution)