I was given a tip many years ago about keeping my knotmeter wheel free of growing things. In your situation? I dunno, but here is the tip. Marine trailer bearing grease and a Q-tip. I smear a light coat on every spring before the boat goes in the water. I would like to think it is just too slick for the zebra mussels to grab onto because in the fall it is still clear of growth and critters. I suppose it could be toxic??