What size tank did you have the RK2 on? I really like the design, but I can't find a single review on it.I've had reef octopus, nyos, aquamaxx and an RK2 X-flo 2.5 (venturi with mazzei injector). The Rk2 is by far my favorite and it rivals the lifereef. The Rk2 is less expensive and there isnt a waiting list. The same model can be plumbed internal or external of the sump and is compatible with a variety of pumps.