I have had my FCV585 going on two months. I use it with an Airmar 264 thru hull transducer at 200kHz. Initially the unit marked fish and worked great. Loved it. It is now to the point where it hardly ever marks a fish. Also the other fishfinder running at 50kHz marks strong fish arches and the same arches on the Furuno are a faint light blue or non existant. The unit is run in Range 120 feet, Auto and Manual sensitivity have been tried. The transducer surface is clean. Any suggestions?