It’s impossible for anyone to diagnose a plant problem from a picture. There’s a number of reason you can get brown spots - from too much or too little of Ca , Mg, Manganese, fluctuating pH, over/under water, spray, disease etc. Take some full plant pictures and give more information on your grow. Is the problem on old or new leaves? Watering schedule, feed & schedule, medium, in/outdoors, spray history, temps, etc. There’s a checklist of info you should post, do a forum search and sure it will pop up.