This thread started in the "Freshwater Polyp" thread and since I don't want to hijack the later I'm posting this separate.
About jellyfish... there is a lady in Las Vegas I think that is a marine biologist and is determined to make jellyfish tanks more popular - Moonjellyfish.com
I talked to her about 1-1/2 years ago and I was impressed by her logical and considerate approach toward popularizing jellyfish tanks. Of course she uses saltwater jellyfish, but only certain kind - one that is suitable for captive life (and are also cold water). I don't remember the exact latin names of the species that she offers but they are on the web site. She breeds the few species of jellyfish that she sells and if I remember correctly she could sell you a jellyfish in any stage of development.
Probably many people know that jellyfish need to be maintained in a constant motion, in a tank that has no dead spots, or tangible suction points. The best tank to provide all that is a specially developed one that is circular tank placed inside a rectangular one - Kreisel tank
. The price is about $10K, but the system that Moonjellyfish was developing in early 2003 would sell for about $6K.
At the time I talked to her she was installing jellyfish tanks in casinos, bars, and private homes. She told me that she travels to the cities where her customers are and spends 2-3 weeks with them teaching them how to operate the special tanks and how to keep the jellyfish alive. Her idea is to start the popularization of jellyfish tanks "on the right foot" because as she said having tanks full of dead jellyfish will lead to a general opinion that jellyfish tanks are hard to mantain, ugly, and not worth installing and maintaining.
Another interesting thing that she said is that actually the jellyfish are not hard to keep but there are a few things one needs to know. Brine shrimp (I think) were the food of choice and she said that several jellyfish could clean the tank from the brine shrimp in 10-20 minutes.
Tankmates could be seahorses and small peaceful fish. Decorations are very much out of the question because of the need of free space where the jellyfish must remain in constant motion. Very much the way to make the jellyfish tanks different are the different colors of light - any color one wishes actually - as well as the outside decoration of the tank - examples
With all these considerations about jellifish keeping jellyfish tanks may seem not that exciting, especially for people with preferences toward freshwater planted tanks. But my observations at the Dallas Aquarium are that the visitors are really drawn to the jellyfish tank and spend a lot of time in front of it. Unfortunatelly during the AGA convention '03 the jellyfish tank at the Dallas Aquarium was not in top shape and the lights were very dim...
The way saltwater jellyfish are kept makes me think that maybe the tiny freshwater jellyfish would need to be maintained in a similar circular tank but a smaller scale one. The single specimen that I saw in one of my tanks was actually moving around by itself with slow pulsating motions. It'd be interesting to experiment with some of these freshwater jellyfish, maybe they could actually be kept in a normal planted tank.