First of all, if you can get in to see Jocelyn at Angling Outfitters in Woodstock he'll teach you everything you need to know about the Lowrance!
There 3 settings you need to adjust regularly depending on water depth and what you want to see.
With the Sonar page active..push
MENU
SONAR FEATURES
On this page you have Noise Rejection, this should read Sonar cone angle, cause thats what it changes, if its set to HIGH, you are using the widest possible beam angle, seeing way more of the bottom than you need to likely, if its set to OFF, its the narrowest beam. If mine is on LOW or MEDIUM I usually see my Balls!LOL
SURFACE CLARITY has alot to do with marking fish, I find if i'm on Lake Ontario Salmon fishing I have it OFF to get good readings on fish/bait.
And of course you need to adjust the sensitivity...
MENU
SENSITIVITY
Hope this helps!