COCONUT fibre soil PH problem

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Hi! So I'm about to repot some seedlings, and thought of using a little mroe exclusive soil this time around.
I found that whole coconut fibre whatever else it was mixture thing, intended originally for orchids, but on checking it's PH levels, found that it was lower, (more acidic) than my previous soil choice, about 4 -4.5 PH.

How come this so highly reccommeded soil medium amongst cannabis farmers needs so much modification, before it's suitable for use?

I live in a European, non-English speaking country, and methods of raising the PH with limestone etc are confusing - I have no idea what the hell limestone is or what its called over here.

I've seen something about Bicarbonate sodium having the same effect though?

:confused: