I run two XP4's in my 180 gallon. I previously used a Marineland Tidepool II wet/dry and a XP3. My water was crystal clear with that filtration combination. When I relocated the aquarium into the living room with new wood floors, I decided to go with straight canisters to avoid any flooding. The XP4's circulate the surface well. However......there is still some white cloudiness I just can't get rid of. The water is clear when looking at the aquarium from front to back, but that haze looking from side to side bugs me. I was considering adding a UV sterlizer with hopes of clairifying the water. I suppose the oxygen level in the water is ok and the biological media (bio chem stars and ceramic rings) are working properly. I still have the Tidepool II and considered putting it in a 40 gallon tank then back under the aquarium. The Tidepool II was a bit noisy with splashing water while the XP4's are super quiet.