I'm running a Bubble Magus NAC 3.5 which is hardly enough for my Reefer 250. I've shopped around and for a small footprint the Nyos Quantum 120 is quite appealing. They're based out of Europe but they've entered a distribution contract with the more familiar Ecotech. Pretty much the same degree of quality and I've heard really good reviews from their products though they don't come cheap...
https://www.marineexperience.ca/coll...rotein-skimmer