Backyard Aquaponics
A place to discuss aquaponics

Adding air,i just thought the counter flow examples although using o2 would work with just air added,the paper i thought was a good insight into how it was done in commercial aquaculture.

counter current and retention time still work with air.

As for the best place to add air, i would say its usually best utilised in the spot where the DO is the lowest in the system because it is more efficient to aerate low DO water than high DO. ie. usually the sump is a good spot for it. But if its emergency air then obviously in the fish tanks.