Gill mites are small parasites that feed off your fish's blood. They do this by attaching themselves to the skin and gills. A sign of gill mites is when your fish spend time at the surface of the water gasping for air. This is because the parasites have latched onto the gills and are causing the fish problems with breathing. On closer inspection, you will probably notice that the gills don't open and close as they should. To successfully kill off these parasites you will need to use Octozin and Sterazin. Check all instructions carefully before applying any treatment.