Guys, try posting some screen snapshots of what you are seeing along with the menu settings you are using (if they are not on the default settings). It’s usually little easier to suggest menu changes if we see what you have been seeing.

The differences between 455kHz and 800kHz on the Side Imaging and Down Imaging units is the same: with the lower 455kHz frequency you are covering a wider area but at a lower sonar resolution. With the higher 800kHz frequency you are covering a narrower area but at a higher sonar resolution (better detail). The lower frequency will also work to a farther distance/water depth.