I have a Helix 12 Mega. When in 2D I am getting a double bottom read in shallower water (15' and less). I have had this on other units and it wasn't a big deal because the false bottom was always showing up below the real bottom. But on this unit it is opposite. What I mean is lets say I am in 15' then the second reading is showing up about 7' and I can't read anything on the 2D screen.

Any ideas? Does this have to do with Chirp?

I will try to remember to take a pic next time I am out

Double bottom readings can usually indicate hard bottom. But there are some issues with bird units doing this.

Set switchfire to clear mode

Turn down sensitivity in shallow water

May need to set depth manually to about 5-10' deeper than actual bottom reading.

Turning off chirp may help also in shallow water

You can also try adjusting the surface clutter as well

I hear about the double bottoms showing up a lot. However, it is most common when you are using 200 kHz freq. If your CHIRP is on, and your freq reads HIGH, switch it to MEDIUM. MEDIUM or MEDIUM/HIGH should be the correct setting.

With a Helix, the unit is broadcasting 200 kHz (high CHIRP) whether you choose to view it or not. It is used for the Depth readout.
83 kHz (med CHIRP) is turned on when you choose to view 83 kHz or 83/200 kHz.