What transducers can/should I buy for my HDS unit?

The HDS transducer choices are the 83/200 transducers in puck and skimmer style. The pucks are easier to use for trolling motor mounts and using in the floor of the boat for through hull installations. The 83 works well in deep water and has a wider cone of 35 degrees.

Doc, I drop shot often, catching fish 40 feet deep or more at times.  I was wondering if you could tell me what your recommendations would be as far as setting the ping speed, sensitivity, manual vs auto depth, etc for getting the clearest picture when drop shotting.  I saw a 2½-pound Kentucky take my bait at a depth of 37 feet during my last tournament, and knew I had the fish on before I pulled into him.  I still feel like I am not seeing all the fish on my display.  Also is there any way to maximize the coverage my graph provides, other than purchasing one of the new Lowrance HDS models.  I am currently using a Lowrance LCX-25.-Thanks, KS, Rogers, AR.

How can I see where the thermocline is on my graph?
You must have the sensitivity set high to see weak thermoclines. Sound is reflected from changes in density so it reflects from rapid temperature changes of the water since water density changes with temperature. This screenshot shows a thermocline or some type of layering of the water even with a low setting on the sensitivity. Notice there is little clutter in the water above the thermocline which usually means the sensitivity is low.