Jay brought up an air issue he has experienced with his build. I agree with what he said that his particular loop design which is quite top heavy and also high volume made filling the loop more difficult. Resonance is optimized for mid towers. We have a detailed write up on loop filling for Resonance because it is a bit different to traditional reservoirs. Make sure to leave the fill tube attached until the air is gone because it is the only way the air can escape (unlike a tube reservoir where it can settle at the top undisturbed). Resonance is designed to push the air to the top but without the fill tube it has nowhere to go and it will recirculate. How long it takes for the air to come out depends on loop design and volume. You can speed up the process by adjusting the pump RPM. We find 50-80% is optimal for the air removal process, higher for larger volume loops. It is quite similar when connecting your inlet to the pump top instead of to the top of the reservoir although this is much slower than Resonance. It causes more air recirculation and slowing the pump can really help to speed up air removal. In the old days we used to use a T-Line to fill the loop no reservoir and it always worked despite it being a worst case scenario for air recirculation.