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How long have you had the clowns? If not properly <<quarantined
>> there is a possibility of a parasitic protozoan. It could also be an anomoly in the color from when the lights are off. Many fish will fade in color when the lights go off for the night as a defense mechanism.
Do the spots look like large grains of sugar on the fish or small translucent flat spots? Fins, body or both? Any other odd observations? FWIW
, the cleaner shrimp will do little to nothing in terms of curing an infested fish. At best, they might keep the population down some but only marginally.