Need help understanding depth finder

[kyron4]

Hello, I have a Humminbird PiraniaMax 210 depth/fish finder. I have never used or seen a fish finder ever so it's all new to me, please forgive my ignorance :rolleyes:

1) when I'm over tall weeds (hydrillia) in say 4'-8' of water, the screen depth jumps around from 2'-4' and somtimes 0'. The weeds and grass can bee seen just below the water surface. The graph shows no bottom just scattered verticle lines. When I get out of the grass it picks up the bottom and show the correct depth. Is this normal when moving over grass/weedy areas in 3'-10' of water ?

2) When moving along in water 20'-25' deep the bottom is flat and the line is at the bottom of the sceen. Then two verticle lines come across the screen and the bottom line moves to the middle of the screen with no change in depth. What's going on there ?

3) there are a few small scratches from sand and such on bottom of transducer. Is this okay ?

Tahnks for the help and again sorry for my ignorance on this matter.

[Bullsprig]

1. yes
2 the lower depth limit has changed
3. Yes

[wannabe fisherman]

the lower depth limit has changed
To add more to this in auto depth mode in shallow water the max depth is say 30 feet. when you get in deeper water the auto mode will reset the max depth to say 60 feet that's why the bottom line changes.