I have a 998 SI Humminbird. I have a few questions. On my normal sonar it always shows a thick color line at the top of the water column but never shows a bottom color or anything indicating where the bottom is and what the contour looks like. Why is it doing this? Secondly, it continues to show fish symbols back to back to back off and on repeatedly at the same depths and it usually is like 2.1 2.1 2.1 2.1 2.1 feet, then it might go to 2.2 2.2 2.2 2.2 something like this. Any thoughts on this. I hate that I spent so much money on this unit and I am too dumb to figure it out and it has not helped me any.