I do have a few artificial sponges because it is nearly impossible to keep those alive in the aquarium, so I get them fake.
They will need regular cleaning and brushing, like once a month or more if your system does not generate too much algae and if they are in a shaded area.
I think that fake corals look very fake, but artificial sponges look quite convincing. Everybody who come to my place, every single person, have always thought they were real.
Both orange sponges here are artificial. It is easy to get them for quite cheap on ebay, just do a search for artificial sponge coral.
