I have done similar (i.e. have a relatively-larger tank subdivided) and attach a piccie of the assembly. The sponge plugs between the tanks are c3cm thick : I can’t imagine much getting through that would compromise the integrity of (say) two different species in adjoining compartments …
… except that I have lingering worries over particularly enthusiastic sperm! This is because there is a current, albeit very slow, from the left-most compartment to the right-most.
Is the possibility of the transmission of sperm from one compartment to the next something that I need to keep in mind, do you think? Or are they so short-lived that it’s not an issue?