looks like nute burn, are u feeding it if not its the soil doin it its to high in nutes,tranplant into some differnt soil if u can, also u can try to raise the cfls a few inches just to make sure its not that but im sure its nute burn
if all u have is mg soil i would put it all into a big bin with drain holes at the bootom and runs alot of phed water through it to helo wash thosde nutes out and then use it,