Mold grows on ice machines like in a petri dish in a laboratory. Its a cool, damp, dark space. I've had luck with regular
cleaning with a bleach solution on land bsed units. The idea is after a few thorough cleanings you can get all the mold spores out and then you will not have much growth for a while until some more outside contamination occurs. There are dedicated ice machine sanitizer solutions but why spend
money on it when you have bleach on hand.