Arduino - water level sensor - help

Hi,

I am tryning to execute the sample in the page: https://wiki.seeedstudio.com/Grove-Water-Level-Sensor/

and I get enconding issue in the serial monitor after the first loop, and then continues like that forever:

11:45:04.705 -> low 8 sections value =
11:45:04.705 -> 0.0.0.****************
11:45:04.705 -> ions value =
11:45:04.705 -> 0.0.0.0.0.0.0.0.0.0.0.0.
11:45:04.705 ->
11:45:04.705 -> water level = 0%
11:45:04.705 ->
11:45:04.705 -> *********************************************************
11:45:04.705 -> ⸮%ХW(R@⸮⸮I⸮&⸮⸮⸮⸮

verifying the code I get the following messages:

warning: “SERIAL” redefined

#define SERIAL Serial

In file included from sketch\water_level.ino.cpp:1:0:

C:\Program Files (x86)\Arduino\hardware\arduino\avr\cores\arduino/Arduino.h:54:0: note: this is the location of the previous definition

#define SERIAL 0x0

Can anyone help?

thank you