Check out my Journal on my Edge build. I changed the filter into a canister filter and was concerned about O2 levels in the water as well. So I used the HOB as a water cascading unit : Cube Nano to 46 Litre Fluval Edge
I mounted canister filter hose intakes and returns to the bottom of the hang-on-back, effectively piggybacking onto it. However, I have quite a large canister filter, (Fluval 305), and I'm concerned that the low oxygen levels have been detrimental to my system. I've had unexplained losses which may be as a result of pathogens benefitting from low O2. I believe it has increased my water temperature as well, (unless that is due instead to my light mods), and it's usually around 80-85 degrees which doesn't help O2 levels either. I upgraded to a 500 series larger impeller for the hang-on-back filter, which seems a little noiser but doesn't seem to have made a huge difference in the current, (too many plants in the way perhaps).