There are many reports across the forums dealing with HELIX MEGA and SOLIX erratic depth issues ...
While there has been no definitive fix found yet - there are several possible things to try ...
*Increase Surface Clutter to 7-8 ...
*Decrease 2d Sensitivity..
*Set Max Depth under the Sonar tab to just over water depth ...
*Turn Off 2d CHIRP to use fixed frequency 2d ...
I have heard whispers that HB may be working on a software fix ...
Rickie