new plumbing

[mark]

You'll be getting head loss (a calculator here) and can always valve back the return but in theory if not using the return pump for display flow, all you really need through the sump is what your skimmer is rated for.

A 1" bulkhead is max'd about 600 gph (work back from here) figure ~300gph through a 1" Durso you'll get some noise but if tuned, fairly quiet. I'm running about 1000 gph split between 2 2" Dursos, not silent but would say comparable to the noise one would get from those little table fountains you see around.

Ideally a Herbie is silent but there is often more noise from the overflow (water dropping over the overflow sides into the chamber) than from the drain itself so need to consider that or find a way to solve (foam block works). For a Herbie you need two drains. Could use one 1" as a primary and if not wanting to return the sump water over the back, do you have room for a third bulkhead (2 drains, 1 return)? The second drain since a emergency backup would be able to be smaller (3/4" if planning 300gph and allowing for primary to become completely blocked). If not wanting to drill a third hole or not wanting to return over the back your limited to a Durso (or similiar type) drain.

Also more differences between the Durso is there's air in the drain so can get gurgling or bubbles in the sump where as there's no air in a Herbie so no gurgling.

I'm happy and with my Dursos and not second guessing but if I was to build again after hearing (or not hearing) a 2-1.5" Herbies flowing 2000 gph, Herbies would be the route I would go.

Bio-balls, seems most just rely on LR in display (no balls in sump).