1/4 what?
I would do the epsom with a regular water, just to avoid any interaction with nutes. But, I've also mixed it with nute water before also, so your call. But, mostly I just add it with plain water.
One application every now and then should do the trick, like every couple of weeks or so. 1tsp for 3L should do you. I do ~1tsp/gallon, but mostly eyeball it. It's not that critical if you aren't heavy handed. LOL, I've been doing this for awhile and generally don't over do things.
Wet