If the only problem you're having is white stringy feces, I wouldn't jump in and treat for bloat. Fish can have light coloured feces for many different reasons.
Should any of them begin to refuse food, spit food, or behave unusually, then you may need to treat.
The epsom salt is a good preventative. You might also feed some medicated antiparasitic food for a few days preventatively, as well. Jungle makes a pellet that contains medication, or you can add some metro to the food you feed before feeding.