Ok, first, check if you have at least the 4.960 update on your unit.
This update was used for this exact problem.
And try using these settings..
Switchfire mode = CLEAR
Surface clutter = 5 to 10 .. but not below 5
Try locking the range to 0-10ft, it's just one click from "auto"
And last, try using only the 200 kHz beam.
Post back your results..
With these settings, I'm able to show reliable, solid depth reading up to 1.5ft of water.