In my 120 gallon, I have one spot that seems to collect fish waste near the back on the bottom. I can only assume it's because there isn't much current in this area, thus waste collects there. So, I purchased a Marineland Maxi-jet 400. Would like a little advice on using it and perhaps placement. For example, place it at the top pointing downward, or at the bottom pointed near the trouble spot? Any thoughts? I have never used a powerhead/circulation pump before.