ok ... i juste try the modification on the sketch but same problem ....
This is what i receive in the Serial monitor when all the sensor is in water.... It's not a sensor problem because if i switch it i have the same result:
Valeur sensor #1: 646
Valeur sensor #2: 15
Valeur sensor #3: 12
Valeur sensor #4: 15
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Valeur moyenne de tout les sensors: 172