Sump Filter Media

[GunnerO]

I've got an older Megaflow Model 2 sump on my 75 gallon saltwater tank. What is the best type of filter media I could use in this sump? The bio balls don't seem to be working. This model doesn't use filter socks. Any help would be appreciated.

[ProAquarist]

Skimmer, refugium, media reactor with purigen and GFO (if reef), and not much else.

Is this fish only or reef?