5.8-6.2 in veg & 6.0 6.4 during flower Is what I run in rockwool. The charts say 5.5-6.5, but 5.5 is really only recommended for pre-soaking the slabs, which tend to be acidic. Below 5.5 Fe becomes highly soluble and is rapidly absorbed by cannabis:

How Far Below 5.5 Before Iron Becomes Toxic?

Iron solubility skyrockets below pH 5.5, and especially dangerous things happen around 5.3 and lower:
pH Level Iron Behavior Risk Level
5.5 Balanced uptake Caution zone begins
5.3 Uptake ↑↑ High risk of Fe toxicity + P lockout
<5.2 Floodgate opens Toxicity likely, deficiency in others guaranteed
<5.0 Game over Complete nutrient chaos, especially in hydro
So yes — 5.5 is not the safe line, it’s the warning siren. Once your res dips below that, especially in low-buffer systems, you're inviting iron toxicity, P starvation, and Ca/Mg imbalance.

Great info!
With peat there's another added problem that you dont have in hydro which is aluminum, it becomes water soluble at 5,5ph and its toxic for the plants and for you and its found in most if not all peat mixes because its naturally present, and not in small quantities. Added to the unproper ph for nute absorption, it can be devastating for the plants.

Eledin said:

As I told you before peat is considered an organic soil, it even has a name, histosol. Peat moss is nothing else than vegetal decomposed matter so its usually around 70%+ organic matter for peat soils. Then I use more organic matter to ammend it but that doesnt mean it wasnt a soil before that. They also sell them as soil in stores, not hydro. No mix is only peat moss as it would be way too acidic, all peat soil mixes are ammended unless you buy peat moss alone. Also I still cant find a chart for synthetic and organic, all I can find is soil and hydro. Please dont be annoyed by my stubborness but I cant say youre right when everywhere I see peat mixes labeled as soil and everywhere I read says the same.

Click to expand...

Peat moss by itself can not be considered soil as it provides no nutrients for plant life ..nada. It's inert. You cannot grow life with peatmoss my itself... No way. It's not a just add water solution by itself. Not a soil.

So seems like we're just chasing our own tails here. And the OP is confused as fuck by now. I'm out. Good luck with your grow OP.

The op will be fine as long as he keeps a 6,2-6,5 ph because while that soil is mostly peat its a soil and no matter if its inert or non inert peat, if you go to 5,5ph or lower with peat youre gonna get aluminum in your plant and lungs because peat has a fair ammount of aluminum and it becomes water soluble at that PH. Peat ash is rich in minerals and while black peat barely releases anything blonde peat is chemically active and while it needs fertilization it interacts with soil ph and releases some nutrients. I think we agreed in the fact that peat needs fertilization, still needs to be treated as soil unless youre using exclusively black peat for hydro. All commercial mixes you find for weed use blonde peat and are treated as soil for ph calibration despite the fact that its mostly peat. You have all the info in google but if you choose to search only for what you wanna see you wont see it all. Also the fact that 90% of peat soil mixes come at 6-6,5 ph and the fact that synthetic nute lines treat peat soil as soil in their charts should be enough to convince you but everyone is entitled to their opinion.

OP is using FFOF, a peat soil that comes with 6,3-,6,8ph. If he keeps it that way he will be fine, preferably 6,5 max.

Thanks again for all the advice & information! I used sledgehammer a few days ago & did a light feed today. Will see what happens.