Welcome bunneh
With a stock standard IBC set up usually the GB sits on top of the FT, a submersable pump in the FT pumps to GB then returns to the FT. Very simple and effective design. The point to note here is the Gb must be higher than the Ft to achieve this.
With a IBC system that incorporates a SLO, the FT overflow must be higher than the GB and also requires a sump. There is a pump in the sump which feeds the FT, there is a SLO in the FT that feeds the GB which then returns to the sump.
Both systems require the GB to be at different heights.
It is still very achievable but requires some simple planning.
Firstly set up the simple IBC system but keep in mind that your FT in this design will later become your sump. So all you have to do is consider at what height will the overflow be from the SLO fish tank. Assuming you will use a full sized IBC for that you just need to make sure the original system is at a height that allows this addition.... or you will have to raise your new SLO FT.
Hope that makes sense.
FT = Fish tank
GB = grow bed
SLO = solids lifting overflow.
