Dennis, I tried two on the back wall with my current tank and from a looks perspective it was great (back wall painted black). I alternated the flow between the two so they weren't working in tandem. Kind of created a wave effect from one side to the other. I finally settled with one on the right side wall, and the other on the back left side. My current tank has a center overflow. You know I'm setting up the same Elos and I'm going to keep the same configuration except routing the dry side cord up from the bottom. I've been able to create a nice wave like this. I don't plan on painting the back wall this time and the bottom glass is so think on these Elos tanks there will be a small cord run visible. I'll be glad to update you after I get the new tank running. JP