Oh man :/ some source of Cal and Mag is just about mandatory for autos and especially if you're under leds. Hmmm, some other roundabout options : Yeah the epsom salts (magnesium sulfate) will halfway well cover your Mag, so you'll have to search for some Cal. Some natural sources are: gypsum rock powder (calcium sulfate), bone meal (powdered preferably), lots and lots of eggshells but they have to be very well cleaned and there's some trick to crushing them up and halfway cooking them on the stove, dunno exactly... There's some calcium in molasses (also known as treacle) but it's not a lot and gotta be the unsulfured kind.