Standard Horizon FF525 User Manual page 29

In very shallow waters when the Auto Gain mode is selected there are
fluctuations in the bottom profile width and its color representation. What
should I do?
In very shallow waters the environment situation (bottom/water condition) change very
quickly thus causing the auto gain algorithm to create oscillations while trying to set optimal
GAIN value for each situation. To avoid this it is advisable to switch to MANUAL GAIN mode
and fine tune the GAIN to a fixed setting.
In very deep waters even setting the GAIN to its maximum value I cannot see
the bottom what shall I do?
Try decreasing the NOISE LEVEL. If still the bottom is not visible there is nothing you can
do, the bottom echo is simply too weak to be detected.
The CPN Series Chart Plotter shows no data when viewing the Fish Finder
page
This may be due to the FF525 having an issue. To confirm, listen to the depth transducer
for the transmit pulse. If the pulse is not heard the FF525 is defective.
CPN and FF525 Operation Manual Page 31