I have had massive issues with the past five or so bags I bought of happy frog, bad enough to contact the company about it.  After interacting with them I refuse to buy fox farms products anymore.
The bags were about 5-10% thumbnail sized river rocks and they all PHed around 4.3, just killed my plants outright after transplant.
Fox Farm's reaction:  Couldn't be our soil, you're mistaken.
I've since switched to a couple of other brands I've had a lot of luck with.  Recipe 420 is a great and affordable option on the west coast, but be sure to let it sit and decompose for a few months before using it.  When I can find it my new favorite is Roots Lush mix.  Lush is a super high quality mix that really doesn't need any extra additives for autos.  It's so rich I would not recommend starting autos in it, but it's great for finishing them.  I grew some outdoor photos in Lush last year that absolutely exploded with healthy growth.  I drive 150 miles to get lush, and it's absolutely worth every penny and drop of gas.