Lots of baby brine!!! Or plankton they feed on is better. As for pelagic species (most are) the tank needs the following:
Constant unidirectional current, no sharp corners in tank, stable parameters, correct temperature for the species,
large surface area-fine mesh strainers that are swept by gentle return flow from filtration to keep the specimens from being impinged are needed for sure.
Cassiopeia jellies from mangrove forests can be kept in reefs as they live stationary on sand bed and use zooxanthellae in the tentacles to supply food. These don’t move though, and resemble anemones. They do pulse the bell, which is upside down on sand. Thus the common name upside down jelly.