I went about 2 years not knowing how to adjust properly or read my Lowrance mark 4. I mostly just used it as a
map and depth finder.
But, the advice that helped me really dial it in this year was a dumb realization that it will help you because it seems so simple.
1 turn off the auto-adjust.
2 set the fishing mode to shallow or fresh water
3 Run the simulator program that is built into the menu settings.
4 Use the Adjust menu to fine tune the sensitivity and the gray line/Color line while the simulator is running to make the screen look the way you think it should look
The unit will save those settings for you automatically.
Making these adjustments before you get on the water will reduce the frustration and allow you to focus on the simple settings of sensitivity and color line.
Of course, with the nasty muddy water we've had around here, any FF is going to be hard to adjust because of all the debris and clutter under the surface.
The short version - use the built-in simulator to dial in your settings offline, then fine tune while on the water.
Hope this helps!
Amateur Kayak fisher and professional geek.