For whatever it’s worth, I have a 12 gal SIP, on its second grow of no-till. Half of the soil was from previous grows, other half new, Coot’s mix. I recycled soil grows and would throw the root ball in my worm bin. Between grows in the SIP I grew a cover crop for 60 days. Recycling soil is fine, even better if you have a worm bin. With no till it’s nice not having to remix soil. I think the thing that works with my system is the composting worms. I use hay as a mulch and that gives the roots more room and food for the worms. Other folks use 15 gal+… I’m digging the SIP, it’s been a huge game changer