I just did a quick Google and first thing that pops up is this ...When using synthetic nutrients, especially in hydroponic and soilless systems, maintaining the proper pH is crucial for optimal plant growth.
Generally, the recommended pH range for synthetic nutrients in hydroponic and soilless systems is between 5.5 and 6.5.
But it's a mute point on this thread, seems like the FF nutrients line is supposedly "organic"?
I get what your saying about the soil, and peat moss by itself is an inert media. Might as well be Coco... Both are inert media. It's when you add the carbon based media (like the Aged forest Product) earthworm castings, bat quano , etc is where it begins to lean towards the organic soil side of things.
If your using the coco or peat moss straight with no inputs then the recommended pH is the 5.5-6.5 for synthetic nutes as your feeding the plant straight away.
If your in organic soil, relying on microbiol activity to feed the plant for you, then it would be in the range on that chart you shared here.
To be honest I just had my head in my ass and saw bottles and just assumed it was synthetic nutrients.
Are they?
Synganics Grow?