My indoor soil was a mix of:
65% 2 different bags of bought garden soil (mostly peat, perlite, etc.)
30% compost; what from wasn't specified on the bag, but I can find pieces of evergreen tree bark in it that couldn't rot because of the resin in it
5% zeolite
As far as I remember I fertilized once, sometime in the middle of vegetation, I usually wait to see some signs of hunger (the cotiledons starting to die). With some universal NPK 6-4-4, diluted 3 times more than prescribed on the bottle. I keep my plants on the slightly hungry side, very few added salts, and so it's easier to keep them happy in small containers. Just watering with tap water all the time.
65% 2 different bags of bought garden soil (mostly peat, perlite, etc.)
30% compost; what from wasn't specified on the bag, but I can find pieces of evergreen tree bark in it that couldn't rot because of the resin in it
5% zeolite
As far as I remember I fertilized once, sometime in the middle of vegetation, I usually wait to see some signs of hunger (the cotiledons starting to die). With some universal NPK 6-4-4, diluted 3 times more than prescribed on the bottle. I keep my plants on the slightly hungry side, very few added salts, and so it's easier to keep them happy in small containers. Just watering with tap water all the time.