Yeah it looks like a type of chemical burn....when my friend of a friend had his plants he used Miracle Gro potting soil, perlite and epsom salt. The end result was a plant that looked like yours. He later on corrected the problem by flushing the soil once a day in the morning. It was the Epsom salt that gave it the brown spots and yellowing leaves. so my theory is that somehow you have a salt build up in your soil or it could be another mineral! but anyway mane, jus try to flush the soil out until the plant looks a lil greener. Then put it on a regular nutrient cycle. ....If your leaves start coming out pale yellow(no brown spots or close to it) that its time for nutrients. Jus' my thoughts!