I have a Koralia 2 (2300 l/h) in my 100g tank. Very happy with it so far. It is very silent & it keeps the water circulating nicely. I am possibly planning to get another one for the other side to get a bit more of a stronger current going. With the added bonus that I can put them both on separate timers & play around with the water movement. In hindsight maybe only one Koralia 3 (3200 l/h) would have been sufficient (?).
I had originally emailed Hydor in Italy to get an idea on which model (they range from 1500l/h to 4600l/h) to purchase. They suggested getting 2 units with lower flow rate (on opposite ends of the tank) rather than 1 unit with a higher flow rate.