You say the system will be 220-240Gal.. How big is the display and what kind of stock are you planning in it? You really should base the skimmer size on the display and not the overall volume since the load is typically concentrated in the display where as the rest of the system (sump and or refugium) contributes to nutrient export.. As such, with a bit more information, it will be easier to provide better suggestions.. The SM250 is going to be too large for your system. I run an SM250 on my heavily stocked 600+ gal system that has a 480g display. I also think the SM200 may be a bit oversized as well. These skimmers have fairly large neck diameters. If you go too big with these skimmers, they will end up being inconsistent as a result. They will skim great at first but then idle along until the dissolved organics build back up enough to produce a decent foam head. The end result is having to run them on the wet side to get any consistency out of them. If you go too large, you will be disappointed. If you properly size the skimmers to the display and load, they are by far the most consistent foam making, skimmate making machines. You are much better off with a properly sized skimmer that works consistently hard vs an oversized skimmer that hardly works and isn't consistent.
If it were me, I'd avoid the Alpha and lean towards the Bubble King Double Cone 200 but without knowing more about your display size and stocking, it's really difficult to be certain.
