You are replying to a 4 year old thread ..... better to start one of your own as people are not likely to notice things in an old thread so you won't get much reponse.
The air trapping is a problem with my Magnum as well. It usually means some gasket is worn out/loose. Try greasing all the gaskets with Petroleum Jelly. If that doesn't work, you can try to find the leaky ones & replace those. <This is usually a problem with the intake side .... maybe the quick release or the intake connection to the canister. One other possibility is that you are sucking air from the tank .... say the intake is next to a bubbler.>
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.