all depends on your LR set up and the size of the PH .. in my 29 right now im using 2 of the smallest koralia nanos. in my 120 i use the following. 2 koralia mag 4s facing end to end, a Koralia mag 3 facing straight forward off the back center of the tank. also have the largest ehiem classic with the spray bar bothering the surface aswell as the largest pro 2 doing the same. dual phosbans running maxijet 1400s with the outlets blowing towards the center of the tank. seems like i have fair flow everywhere in my tank and no dead spots