What transducer do you have? 83/200, 50/200, or some sort of CHIRP transducer?
If you have the 83/200, which was commonly sold to bay fishermen, I found that transducer on my dad's old boat to be useless at 83kHz. Stick to the 200kHz.
You can check some Youtube videos on how to set up your Lowrance here too:
https://www.youtube.com/results?sear...hfinder+set+up
I know a lot of the videos encourage a lot of gain to be turned up to "see more fish". I tend to think that some want their gain turned up so high hoping to see fish that arent there. While i like to see fish, I also like my unit adjusted so I can try to differentiate bait from game rather than trying to pick up every little fish. Sometimes when you turn your gain up too much the marks fill in not giving a clear picture if there are actual gamefish around bait.
Here is some info to try to help you understand your fishfinder...
http://www.cbangler.com/showthread.php?t=3048