I think I know the answer to my question but want to check without having to dive in. I set the surface clairity to low and I see a red block at about 5 feet never goes away. If I set surface clarity to high it is mostly gone. Same for sensitivity, up over 55 I see it strong but down around 36*40 it is mostly gone. This lake was 52-54 degrees and tea colored water on a bright sunny day. I keep seeing fish arches just above this red blob running across the screen but I never caught a fish at that dept or above. Was this the thermocline?