@Richard Drysift has some great input, certainly should be noted
some of us may not want to spend $80 in soil ingredients to recharge $25 worth of soil though, like myself. I just run four 3g pots in a 4x4, I dont need a lot of soil, and i dont want to buy new every run.
between runs i add azomite (volcanic ash) and dolomite lime (ph buffer).
i use dry salts dissolved into water. regular feeding provides all the nutrients the girls need
this has worked for me. best of luck to you