i have two plants that are starting to develope brown all over the leaves starting at the bottom of the plant and slowly working up. the leaves are also turning crunchy and slighlty curling under around the edges. these are in foxfarm ocean forest soil mixed 50/50 with perlite. also i flushed them real well about 5 days ago and it seems like its progressing. is this possibly mg deficiency? if so and i add epsom salts how long will it take for them to get better? thanks in advance.