use GreenAll organic soil for supersoil base?

Wats good everyone I'm a total newb to organic supersoil, Ihave used organic soil with adding nutes for its needs but I now wanna try.n stay away from bottled nutes. Anyways my main concern is I'm planning on using greenall organic soil its heap and available here to me in my small town. It has kelp meal, greensand,pete moss,bat guano,ewc, and a.few extras, ill post a pic of the bag when Ican. So how much more castings do I add to make the tga supersoil if it already has some in it already, and is this good soil? I do add perlite to the soil. Any help would ease my mind. Oh n I'm mixing 2 bags for the supersoil

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Its made by e.b. stone. A ready-to-use all organic potting soil formulated for growing indoor and outdoor plants in containers. Contains Fir bark, Canadian sphagnum peat moss, composted mushroom soil, volcanic pumice stone, earthworm castings, sand, feather meal, bat guano, and kelp meal