To the left is a 2nd sump that I was using for a 2nd tank that I set up downstairs. But initially, it was my QT for new fish, as well a refugium with caulerpa and chaeto.
I had it connected to the sump using this DIY overflow. It had an airline connected to the intake side of a pump in the sump which made it basically foolproof. It prevented the syphon from ever breaking, and would self prime if the power went off.
