How to Clean a Transducer

Use a soft cloth and mild household detergent to clean a transducer. If the fouling is severe, remove the growth with a green Scotch Brite pad. Be careful to avoid scratching the transducer's face.
It is possible to wet sand a paddlewheel on the speed sensor with a fine-grade wet/dry paper.
If growth appears frequently, apply anti-fouling paint (water-based) to the transducer's bottom once every six months. Check with the local marine dealer or local hardware store for anti-fouling paint.