By the way Jellyfish don't make good pets. they are very hard to keep.
They require some specially modified aquariums called Kreisel, that are usually very expensive and complicated. Although not all species require such an elaborate aquarium, the species with long tentacles do.
To minimize damage the water flow in these aquariums not only has to keep the Jellyfish in constant suspension, but also be discharged in a very broad and evenly distributed manner. Water leaving this aquarium must be done in a way that doesn't allow the Jellyfish to be drawn into these overflow.
Filtration is similar to a Reef System and water must be free of nutrients and ticulate matter. they are invertebrates they will not tolerate any forms of toxic metals, like copper. Water temperature of most Jellyfish ranges between 58 and 62 degree's, thus requiring a refrigeration system or chiller. each species is different, so this range may vary.
they require a huge amount of live food. In nature, they eat plankton and algaes. In captivity this food must be cultured, and these they need to be fed a variety of algaes greenwater, and brine-shrimp. but, hey! I may br wrong