FF spoil is already Ph balance and can be messed with a little but I found it's pretty loaded as it is.
Mixing your own soil is easy and well worth the effort . A good base would be coco , worm casting , soil , compost of some sort and perlite . From that base you can start playing with amendments .
Basic mix:
Coco coir
Worm castings
Soil
Perlite
Mushroom compost / kraail mix
Kelp meal
Bonemeal
Rock dust
Lime
Mycoroot
FF soil is nice but it's ready easy to replicate at a fraction of the price