You will find little you want to use at lowes. Do you have a garden or farm supply store handy. A big ole bag of perlite is your friend. Too much is almost enough.
Be careful witb MG soil. The more water, the more nutes released. If you over saturate with water, you can burn the plants. You also don't want to go straight into it, in my opinion, with a clone, seed, or seedling. I use MG seed starter for that but mix it with about 30% plain perlite (not MG) from a garden store. Shit is also way cheaper at places that supply farmers! I got a 30-40 gallon bag of perlite for $15 as I recall.
I personally make my own mix and like it to have no nutes so I know what they are getting. It does come down to reading the plants. That is the hard part with soils full of nutes, you can't back off or feed plain water if need be.