Peeling it off tupperware should be easy compared to removing them from rock work. Just start at an edge and using you fingernail very gently work an edge up, gradually you should be able to work it free. If it is only attached to the plastic, take it out of the water and work on it. If I am able to take them out of the tank I do, it is much easier.
How big is it? I think it needs more circulation than it is going to get in a tupperware container w/ holes. How about a strawberry basket?