If it is dual beam, you want it set on 50 mhz not 200 for water less than 60 ft deep. You can adjust the sensativity according to conditions. when you are on perch, you should see 10 or more medium size arches on the screen at a time. If you turn up the chart speed, this could help as you might see movement on the screen. Perch are almost always within 3 feet of the bottom. You can drop an object such as a rock or brick attatched to your line, below the boat to try to follow it and see how it looks and make adjustments accordingly.