We have a 30g JBJ rimless reef and I tried a koralia 850....& ....1050 cuz I had extra from our main 150g reef----> they were WAY to much flow, the fish were like in a tsunami....
I then tried the koralia 240 nano circ pump and it was not enough
so finally put in the koralia 420 nano circ pump and itworked perfect..
the sump still has the 2 main pumps that came with the tank too.