[Gerry Zagorski]

You might try and adjust your gain manually rather then leave it on auto. Best way to do this is take it off of auto and manually set your range for twice the depth you are in..... Now adjust your gain so you have a faint 2nd bottom reading. If your are in 15 feet you should see it at 30, in 20 feet at 40 etc...

Now adjust your range to whatever depth you are in and see if that helps.