from my understanding epsom salts contains really high lvls of magnesium and not such high lvls of calcium which can ultimatly be bad for your plants...its a quick cheap fix for SOME people but in no way shape or form a alternative to a quality horticulture grade cal/mag solution
not sure if you have a Agway nearby or a hydro store but they will both offer a hroticultural grade cal/mag solution you can just add in with your waterings.
also if you pick up a bag of espoma garden lime (available at Agway) that had cal/mag in it already and will help maintain a stable soil PH...
my mix using fox farm ocean forest is as follows
1/2 bag Espoma garden tone organic fertilizer
1 bag FFoF potting soil
1/2 bag organic perilite
1/2 cup espoma garden lime
this mix has proven reliable over the past 2 grows no additional fertilizers are really needed untill week 4 of flower, i usually do one dose of veg nutes at about week 4 of veg then start my bloom nutes around week 2 of flower, probabally not necessary but im 100% organic so over ferting is pretty rare occurance.
hope this helps
RMTB