I know fishfinder questions are beat to death BUT I need help I think ... I got a pretty good deal on a humminbird 210. I installed it and took it out today. The lake I tested it on ranges from from 3 - 9 feet. The FF worked ok at first in 7-9 feet, it showed a few fish ... but at less depths nothing. Just a faded out eratic scroll. Is this because of depth or possibly poor install? I mention poor install because I did have problems getting the transducer set using marine goop.

Thoughts .. suggestions?