I'm using the Avast skim mate locker. Works well. Drilled a 2 inch hole just above the sump through the dividing wall. I also run the dosing lines through this hole.Curious to know what people with the reefer 525xl are doing for external skimmer collection? the sump that comes with the tank albeit nice and functional leaves zero room to put some sort of collection container that's connected to the skimmer collection cup to prevent overflowing back into the sump. As far as I know my only option is to drill into the stand a hole lower than the collection cup for gravity to allow it to drain into a container that unfortunately will have to be housed somewhere other than the sump part of the stand.