[MsCowpea]

Unfortunately, most hydro stores charge a lot of money for Promix. So do some comparison shopping.

Walmart is carrying a homeowner Promix line
in a red or yellow (organic) compressed package which makes
2 cubic feet for $12.88.
You could add a little more perlite for a higher porosity. And the pine bark if you can find it to put together Raybo’s 3-2-1 mix. I don’t know how the quality compares to their professional line of potting mixes like Promix BX
(Popular with EarthBox users) or Promix HP (more perlite for higher porosity).

I use metro mix products (and some Promix as well). MM 360 is for filling small seed cells. Particle size is fine so the drainage is low and water
retention high.