Are you talking about a tank with only one ray? or like an exhibit type setting at an aquarium? Usually rays that are use to having their tanks clean would be desentisized and likley leave you alone while cleaning. For a single ray in a home aquarium, I'd say it would depend on the ray. If you go to clean it and it appears to be aggitated I would ease into cleaning and use long brushes etc. and see how the ray responds over time.