I start with an expensive, non fertilized potting soil and add 20% perlite, and sometimes 10% vermiculite. Do not put clay pellets in the bottom for drainage. It will hold water there and promote mold, rot and mushrooms. Some clay pellets mixed in the soil is good though. After a couple weeks I start adding (slowly) hydroponic nutrients with waterings PH'd to 6.8.

I've found that using the above techniques the soil is about 6.7 or 6.8 PH, which is a good thing. If yours is not, you need to fix that. To find out, do a soil run-off test or buy an expensive soil meter (not the cheapo ones). For the run off test, when your soil is pretty dry, soak it with PH 7 water and catch the first run-off to measure.