flow questions

[mark]

You can push a lot through a sump, I had 2000gph (now lowered to 1000gph) with my 75g sump, just need to be prepared (bubble towers, filter socks, foam blocks).

For the OP, I'd just keep the return you have now, give your Koralia's a try. If looking like you need/want more flow, add another or switch to higher flow PH (Tunze Stream).