New2reefing

For a 55g, you will need a narrow sump usually, something maybe 10" wide front to back. The longer the better.

For that tank, an submersible pump like the Eheim brand would be ideal.

Thanks for the help. One more question, is it better to build one from acrylic or use a 20g long glass tank? I have been looking at all kinds on the internet. I want to do a fuge. How big should each compartment be?

Knowing of Marc's fondness for acrylic.. he'll probably suggest that! Unless you know how build with acrylic well, I would recommend on glass for the cost alone as having one made for you won't be that cheap. If money isn't much of a factor I would recommend an acrylic one for for it's extra flexibility, strength, and weight.

As big as you can fit. Zones should be based upon the total sump, divided to hold the skimmer snugly and then the rest is refugium & return. Avoid a tiny return zone, those are nothing but a headache.