Question regarding lifereef overflow and sump gph

[saltines]

So i have a 180gallon undrilled tank. After some reading and reccomendations. Ive decided not to drill and buy a lifereef HOB overflow box instead. They recommend buying a double siphon box and a 1200-1700 gph pump. I will be using a 55gallon sump/refugium and need to account for about 5 feet of head loss.I guess the general rule of thumb for sump circulation is 3-5 DT volume..

Am i correct in saying i need something around 1800 gph for the display tank circulation and 600-800 gph in sump in order for proper filtration? If thats the case then why do they recommend purchasing a 1200gph overflow?

-Also is there any recommended pump brands-Im looking to buy a submersible

[EllieSuz]

Jeff at Lifereef has been doing this for a long time. I stayed with every recommendation he made and have never been sorry. Buy whatever he suggests is my best advice.