I have two mollies hanging at the top of the tank. It's a 120 gal. tank and I have about 30 fish and these are the only two that are acting like this. I had turned off the aerator for a day since it made feeding difficult. I have a fluval fx5 filter and have one of the spouts going to the surface to move the surface. The tank is also planted with live plants and I do a 25% water changed twice a week. All my numbers are good.