My 10 gallon aquarium had an oily film at the surface that the filter couldn't clear up. I ordered the Aqua Mist 5 1/2" stone along with a Tetra Whisper 10 air pump. It works great, producing bubbles all along the surface (needs to be flat.) It is fairly heavy, and has edges that can be covered with gravel, holding it in place. (It can be placed completely under the gravel as well, but I have it level with the gravel surface.) I run it for a couple of hours a day, and the water is crystal-clear, has never looked so good. The fish look healthier, have great color, and are more active. The tetras love swimming through the bubbles, and the plecostomus will sometimes lie directly on it, fun to watch. It adds considerably to the current in the tank, and the fish are thriving. Great product!