HEY, what you got in that soil mix?
This what's in Plagron Light mix Composition is in order of greatest size first, although no percentages are given of each constituent part.
Peat moss is fairly acidic so addition of lime will be needed to raise the PH to the 5.5 - 6.9 PH range, dolomite lime has the added benefit of containing mag.
As it states mineral fertilizer is 1.5 kilos per 1 meter cubed, if you are making your own mix make a box 10cm cubed fill it with your mix and weight it (mix should be very slightly moist, rather than 100% dry and deffinitely not wet, you should not be able to squeeze and see water dripping) this size (10cm cubed) is 1/1000 of a meter cubed, which is a liter and will need 1.5grams of 12-14-24 feritlizer added.
Organic contents is 80% which leaves the inorganic contents at 20% this is the perlite, lime & fertilizer content .
So a 50 liter mix will contain roughly 40 liters of organic mix (white moss, black peat moss & peat moss fibre) ,10 liters of perlite and 75 grams of powered fertilizer at 12-14-24 NPK & lime which is roughly added at approx 0.25 parts to every 10 parts of mix (1 part to 40 parts mix). Start with less lime you can always add more but you can't take it out once in the mix.
This is as close as I can offer, compost mix manufacturers do this for a living. A little trial and error on you part will be needed if you wish to replicate this mix.
Want to ask plagron anything contact the service desk -
servicedesk@plagron.com