It´s a very drastic step to add Epsom salts for a little problem like that..

Do what latewood said... FLUSH and start over with a light EC value of 1.1-1.2 and a higher PH of 5.8. Maybe try flushing with Enzymes.. good for the damaged roots, it´s strips the roots and makes it nice and strong again. Best Enzymes IMO oppinion are the enzymes that disoves wasspaper glue best. I´ve got great results with the PLAGRON enzymes.

Oh yeah..

Buy a EC and PH meter.. it´s sure helps you adding the right amount of nutes