promix is a premixed fairly neutral medium with no nutrients. adding extra perlite yourself is optional. perlite perlite perlite, you cant go wrong with it.

i dont think you should worry too much about mixing soils if you use water soluable fertilizer when feeding regularly with teas.

i searched the web for supergro, but couldnt really find anything (56k connection) supergro <--proper spelling???

also.. ive never had a problem w/ schultz organic potting soil. extra perlite of course.