If you have the space outide the box, then I prefer external protein skimmer. Installed with easy access unions to pull out if needed. Some problems with internal are, difficulty in doing periodic maintenance, and dealing with encrusting creatures and coralline algae, if it's not shielded by lights of a nearby refugium. These usually 1st compromise the internal pump, and can lead to early pump failure. So IMO, if you have the space and good access then external, if you don't, then try to place prior to refugium area, and shield from light.[emoji106][emoji4]