Tony is right on. I have the 2228 (the old model) on a 75 gallon tank and its almost too much. It should be perfect on a 100 or even a 125. You probably won't need to clean it for 6 to 9 months with all that space inside.
By the way, I bought it in 1999 and it still runs like it was brand new.
Put the spray bar on one side of the tank with the nozzle pushing the water out horizontally just beneath the water surface.