Advice

First let me say I’m happy to return to the hobby and this forum after a 6+ year lay off. Seems a lot has changed in my time off with technology, lighting , filtration. About 2 months ago I purchased a Red Sea max 130d for a great price, at first I was a little skeptical about this whole All In one idea but I figured with all the advances I would give it a try. Never the less I am not happy and I’m in the middle of building my sump/refugium because I can’t seem to control my nitrates. All other paremeters are spot one other then nitrates. So I purchased a Eshopp PF 300 overflow and the Jecob dsc3000 returns pump. With the one inch overflow what size piping should I use for returne? Don’t think I need a valve on returne being the jecob comes with a flow control. Thank you for the help and happy to return. By the way it’s a 20 gallon sump I’m building.