I'll have to agree with Aaron. You will want to put your powerhead in a place that gets you the most current in your tank. I don't know your setup. But I would suggest multiple PH's. You might want to have one just for the area behind your
LR.
A great idea a friend of my had was to take a PH, point it down. Run a piece of
PVC to the bottom of the tank, elbow and attach another
PVC along the length of your tank. Cap the end and drill small hols along the Horizontal
PVC. This will use one PH to distribute current throughout your
LR.
I've got a bit too much
LR to do that now but if I ever move my tank or get a larger one, I'll be fitting it with this setup.