Jabba,
I have a HDS8 as well, as others have said the sensitivity on the units is very touchy, if your not sure what you are seeing you can change the display colour back to black and white, have a look at what you are seeing and then change to colour again.
Or change the colour scheme to 1, which is the standard lowrance colours and use that as your base, as there are quite a few images in this section showing that colour scheme.
as a starting point leave the unit in auto mode, until you gain a little confidence, then range and sensitivity will be your friend.
Regards
Honda.