Steralising and re energising soil/compost/not coco

At the risk of sounding stuuuuupid. . .
I want to use potting mix so not to bother with adding lemon juice or vinegar to every watering/feed. But I also don't like gnats too much so I figured I'd try and nail those suckers before planting.
Does anyone have any tips for re energising the media with beneficial microbes after a cleanse?
Cheers in advance

Just add a form of active compost, fertilizer, and a mineral inputs. For example: worm castings, chicken manure, and dolomite lime and/or garden gypsum. Hydrate and let it set for 3-4 weeks.

Richard Drysift said:

Just add a form of active compost, fertilizer, and a mineral inputs. For example: worm castings, chicken manure, and dolomite lime and/or garden gypsum. Hydrate and let it set for 3-4 weeks.

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Oh yeah, worm casts! Why I did I not think of that. Cheers pal !

Piss. It's free