If you do F & D or RTW, it is totally uneccessary to areate your reservoir.
The moment that water comes out of a tube and get in cpntact with the air, it will have maximum DO.
The only reason why one could use a circulationpump in your reservoir, is to make sure that your water and nutrients are mixed well.
For the rest, no need at all.
Maxium DO is soooooo easy to reach.
Besides that, there is oxygen around your roots when they are not flooded.
If the roots are just damp, they will uptake so much oxygen in gaseous state.
The moment the roots get flooded, the roots will uptake water and oxygen (DO).
And after the drain, enough small waterdrops are around your roots, and also enough oxygen.
Oxygen in gaseous state is hundreds of times more effective, which the roots will uptake because of the film of water around the roots.