Need Help. Raymarine C120

[The Mitigator]

Looking for advice. I have a Raymarine C120 Wide digital depth finder. Looking to find the best gain setting for fishing the bay. I currently have it set at 50%. I set it at 17% and it would not show bottom line. What have you found?
Chuck

[27 sailfish]

General rule of thumb.

Turn the gain almost all the way up when in about 25 feet of water. Yes , the screen will be filled with clutter. Slowly turn the gain down until the snow/clutter just goes away. Most units will be 60 to 70 percent.

You sometimes will need to increase or decrease the gain when in deeper or shallower water but most times you can leave it alone.

Using the manual settings gets you the best results.