Future soil composition

[purepotstill]

Hi guys,

 

I may launch another grow, probably two plants (autos) more to be sure to have enough weed for the year to come.

 

I'm doing my soil from non specific compost, as I don't want to buy these things online. I'd like to have some advice about what to add. 

 

Here some infos written on the bag : composition is pure peat compost, mixing frozen brown peat and blonde peat. Ph is 5.8. Water retention in 850 ml/L, air retention is 50. Resistivity is 1050 ohms/cm. It's said it has enough nutes for 4 weeks, but can't find any npk ratio, even on the maker website. It's really light and fluffy.

 

I add vermiculite to improve it, maybe 15%. Added a few clay pebbles at the bottom on my last grow, but won't do it anymore as I read here it's more of a bad thing than a good one. Perlite doesn't seem to be available near my home, nor coco. Had dome decent crops last time, so it must be an OK soil, but I'm searching ways to improve it. So do you think my standard compost good for marijuana ? And what would you guys add to this base ?